OBD2 Codes: Which Get a Software Fix? 1,412 Manufacturer Bulletins Analyzed

When a check engine light comes on, the conversation at the counter is almost always about parts: a converter, a sensor, a thermostat. The manufacturers' own bulletins tell a different story for some codes. We read every one of them.

On 17 September 2026 we took NHTSA's public file of manufacturer communications received from 2015 to August 2026 and pulled every document whose summary names one of 17 common check engine codes. That leaves 1,412 distinct bulletins from 15 manufacturer groups. We then asked one narrow question the file can answer reliably: how many of them are software updates?

How to read any OBD2 code

Every code in this index, and the five-character code a scanner shows for the check engine light, follows one format set by SAE J2012, Diagnostic Trouble Code Definitions. We quote its April 2002 edition, the edition federal emissions rules incorporate by reference, as listed in 40 CFR 86.1. The code "consists of an alphanumeric designator, B0 -- B3 for body, C0 -- C3 for chassis, P0 -- P3 for powertrain, and U0 -- U3 for network communication, followed by three characters." Read P0420 from left to right and each character narrows the question.

First character: the system. P is powertrain, the engine, emissions and transmission ranges listed below. B is body, C is chassis and U is network communication between the car's control modules.

Second character: who wrote the definition. A 0 marks an ISO/SAE controlled code, one of "those codes where industry uniformity has been achieved", so P0420 has one standard number and message for every maker that uses it. A 1 marks a manufacturer controlled code, the kind that "will not generally be used by a majority of the manufacturers due to basic system differences, implementation differences, or diagnostic strategy differences." The practical rule: look up a P1 code in the maker's own definition. Our P0325 guide shows why: on a Hyundai or Kia the knock sensor is also a bearing-failure alarm with its own code, P1326, and a very different price.

Third character: the area of the car. For P0 codes the 2002 edition assigns the ranges like this:

• P00: fuel and air metering and auxiliary emission controls
• P01 and P02: fuel and air metering
• P03: ignition system or misfire
• P04: auxiliary emission controls
• P05: vehicle speed, idle control and auxiliary inputs
• P06: computer and auxiliary outputs
• P07, P08 and P09: transmission
• P0A: hybrid propulsion

Last two characters: the specific fault. Within an area, "display characters 4 and 5 allow up to 256 code definitions", because "Some ranges have been expanded beyond 100 numbers by using the hexadecimal base 16 number system." The third character is hexadecimal too, 0 to F, so a letter can follow the P0, as in the P0A hybrid range.

Put together, P0420 reads: powertrain, standard definition, auxiliary emission controls, and 20 for the specific fault, which our P0420 guide explains as the catalyst system on bank 1 reading below its efficiency threshold. The standard defines the bank too: "bank 1 always contains cylinder number 1, bank 2 is the opposite bank".

What a code is not. Codes "are intended to be used as a directive to the proper service procedure", the standard says. A code points to a test, not to a part, which is the argument of this whole index: the same code can end in a new sensor, a software update or a new exhaust clamp, and the test, with any bulletin for that exact car, says which.

Every code with a full PulsCar guide

We have a full guide for 63 codes as of 30 October 2026, including all 17 codes in this index, shown in bold. The group column is the name SAE J2012's 2002 edition gives the number range, a filing label, not a diagnosis.

For a code that is not in the table, the reading rule above still gives you the system, whether the definition is generic or the maker's own, and the area of the car to start in.

The short version

What did the PulsCar Check Engine Code Index find? That software is a far bigger part of how manufacturers fix check engine codes than a parts counter suggests, but not evenly. Of 1,412 distinct bulletins received by NHTSA from 2015 to August 2026 that name one of 17 common codes, at least 639, or 45 percent, describe a reprogram, reflash, calibration or logic update. Stellantis publishes many separate flash bulletins, so we report every share without it too: the floor is then 213 of 911, or 23 percent. The code that stands out either way is P0128, coolant temperature below thermostat regulating temperature: at least 74 percent of its 125 bulletins are software, and 52 percent without Stellantis. At the other end are evaporative leaks. Outside Stellantis, P0442 and P0455 together have two software bulletins in 76. Underboost, camshaft timing and low fuel pressure codes sit between 10 and 17 percent.

How did PulsCar count software updates in manufacturer bulletins? With a published rule applied to the summary NHTSA stores for each bulletin, then checked by hand in both directions. A bulletin counts when its summary says it reprograms, reflashes or updates the engine, transmission or ignition control module, changes a calibration, revises control logic, or starts with the word Flash, as Stellantis flash bulletins do. We read 30 randomly chosen flagged bulletins: 28 were plainly software updates and the other two made reprogramming conditional on a part number or calibration table check. We also read 40 randomly chosen bulletins the rule did not flag. Two were clearly software, Kia campaign SC114 and GM PIP5905, and 14 did not say what the repair was. That is why every share on this page is a floor, not an estimate.

Does a PulsCar index software share mean a code is usually just a software problem? No, and the difference matters when you are standing at a service desk. A bulletin applies to particular models, engines, build dates and symptoms, and many software bulletins also require an inspection or a part. The index measures what manufacturers wrote to dealers, not how often a repair succeeds and not how often a part fails. What it does support is a practical rule. For codes with a high software share, especially P0128 and to a lesser degree P0420 and P0171, ask the dealer to run your VIN for open bulletins and software updates before approving a thermostat, converter or sensor. For codes with a low share, such as P0442, P0455 or camshaft timing codes, the fix is far more likely to be physical, and a proper test matters more than an update.

The index

Seventeen codes, chosen because they are among the most searched OBD-II codes or appear most often in our guides. Software, at least is the share of distinct bulletins our rule flags. Without Stellantis removes Chrysler, Dodge, Jeep, Ram, Fiat and Alfa Romeo bulletins. Coverage counts bulletins whose summary mentions special coverage, a warranty extension or an emissions campaign. The last three columns come from NHTSA's complaint file: complaints naming the code, median reported mileage and the code most often named alongside it.

A bulletin that names several codes appears in each code's row. Without Stellantis, P0441 has 17 bulletins and P0401 has 31, so treat those shares as rough. Median mileage is the owner-reported odometer in complaints that give one; for P0174, P0401 and P0442 fewer than 15 complaints report mileage.

Finding 1: P0128 is the code manufacturers fix with software most often

P0128 means the engine computer expected the coolant to reach a warmed-up temperature and it did not. The instinctive repair is a thermostat, and sometimes that is right. But in the bulletin file, at least 92 of 125 P0128 bulletins are software updates, and the pattern is not a Stellantis artifact: without Stellantis, 32 of 62 still are, led by Hyundai with 10, Kia with 9, Ford with 5 and Mitsubishi with 4.

The reason is built into the code. P0128 is a judgment the computer makes from a model of how fast an engine should warm up, and manufacturers revise that model. Ford TSB 25-2486 says a P0128 lamp "may be due to the software in the PCM." Mitsubishi campaign SC-26-003 reflashes the engine computer for P0128. GM's 22-NA-054 corrects a calibration timing error on 2021 crossovers; our rule does not flag it, which is one more reason the share is a floor.

Software is not the whole story. GM's special coverage N252508350 replaces the thermostat on certain 2021 XT5, XT6, Blazer and Acadia models for 15 years or 150,000 miles; its NHTSA summary does not name the code, so it is not in the count. The index says to ask about an update first, not that a thermostat never fails. Our P0128 guide walks through both.

Finding 2: emissions-monitor codes lean software, but check who is publishing

P0420, P0430, P0171, P0101, P0401, P0441 and P0456 all come from monitors that compare sensor readings with expected values, and all show software shares of 46 to 74 percent overall. Much of that falls away without Stellantis, which publishes many separate flash bulletins that each list dozens of codes. P0456 drops from 72 to 21 percent.

What survives is still useful. Without Stellantis, about one P0420 bulletin in three and one P0171 bulletin in three are software updates, and P0101 stays at 38 percent. Examples we have opened and read:

• GM 18-NA-331: reprograms the ECM on 2013-2015 Trax and Encore 1.4L models for P0420.
• Ford TSB 25-2188: a PCM software update for P0420 on 2022-2024 Explorer 2.3L models.
• Ford TSB 23-2195, superseded by 25-2342: PCM software for P0171 on 3.3L F-150s.
• Honda 20-100: for P0420 or P0430 alone on the 2016 Pilot, update the software and test the injectors, with the warranty on the repair extended to 10 years or 150,000 miles.

The P0420 and P0171 guides explain the non-software causes, which are still the majority.

Finding 3: leaks and mechanical faults are fixed with parts

Where a code describes a physical condition the computer measures directly, software is rare.

Evaporative leak codes are the clearest case. Outside Stellantis, P0442 has one software bulletin in 36 and P0455 one in 40. The bulletins are about caps, filler necks, canisters, valves and test procedures: Kia TSB FUE040 replaces a canister close valve that sticks open on the Rio, and GM 23-NA-073 addresses dust getting into the evaporative canister. Our P0442 and P0455 guides cover how technicians find the leak.

Boost, camshaft timing and fuel pressure codes sit between 10 and 20 percent without Stellantis: P0299 at 10, P0011 at 12, P0087 at 17, P0016 at 20. Ford TSB 25-2200 traces misfire codes with a ticking noise to worn camshafts and tappets, and GM's P0016 information tells technicians to check whether the crankshaft reluctor has moved. The misfire codes, P0300 and P0301, fall to 20 and 17 percent.

Finding 4: where the warranty extensions are

27 of the 1,412 bulletins mention special coverage, a warranty extension or an emissions campaign in their summary. That is a floor too: GM's thermostat coverage N252508350, for one, does not name a code in its summary. By code, P0301 has 7, P0420 has 6, and P0171, P0101 and P0300 have 5 each. Three patterns stand out:

• Misfires from piston rings. Honda bulletins 13-078 to 13-082 cover rings that rotate and foul spark plugs on several 2008-2013 models; all five name P0301.
• Catalyst codes the computer gets wrong. Honda 18-022 and 18-023 extend the warranty on 2006-2007 Accord Hybrids whose ECM misreads sensor inputs as converter deterioration and sets P0420 or P0430. GM special coverage 15821 covers an exhaust clamp leak that sets P0420 on 2013 models for 8 years or 80,000 miles.
• Lean codes from the PCV valve. GM special coverages N202299080, N192210230 and N192291620 replace camshaft covers with cracked PCV diaphragms on 1.4L and 1.6L engines; N202299080 alone lists about 810,404 vehicles, covered for 10 years or 120,000 miles.

For a driver, that is the second question to ask after software: is there coverage for this code on my VIN?

Finding 5: what the complaint file adds

NHTSA's complaint file is a different kind of evidence, owner reports rather than dealer instructions, and it adds two things the bulletins cannot.

When the codes show up. Among complaints that report mileage, P0420 has the highest median, 109,057 miles across 98 complaints, consistent with a converter-efficiency monitor that trips late in a car's life. P0299 underboost, 65,000, and P0128, 67,650, show up earlier.

Which codes travel together. P0420 and P0430 are named together in 24 complaints, P0171 and P0174 in 15, P0300 and P0301 in 94, P0016 and P0017 in 42. A pair like that usually points to one shared cause rather than two separate failures, which is the logic our guides use.

Finding 6: software is a growing share of the fixes

We split the 1,412 bulletins by the date of their latest version. The software floor rises in each period, and the rise survives without Stellantis.

Two cautions keep this from being a headline. The last period is 20 months, not five years, so its 96 bulletins outside Stellantis are a small base. And a bulletin revised in 2025 is counted in the last period even if the original came out years earlier, which pulls long-running software campaigns forward. Even so, the direction is consistent across all three periods and both columns, and it matches what the documents describe: newer bulletins increasingly fix engines by changing how the computer judges a sensor, not by replacing the sensor.

The codes differ in how their bulletins moved over time. Catalyst efficiency codes kept appearing: P0420 has 53, 48 and 42 bulletins across the three periods, and P0430 went from 23 to 29 to 30, its busiest period being the shortest one. Evaporative codes faded: P0456 dropped from 158 to 100 to 11, P0441 from 48 to 30 to 4, and P0455 from 33 to 33 to 3. Lean mixture code P0171 fell from 64 to 31 to 10. Misfire code P0300 stayed heavy in every period, with 202, 146 and 83; 20 of the 83 in the last period are Honda and Acura bulletins on reduced cylinder head gasket effectiveness.

Finding 7: manufacturers differ, and not only in what they fix

Software shares differ sharply by manufacturer group. Part of that is engineering, and part is how each company writes the summary NHTSA stores, which is all our rule reads.

Stellantis publishes software one bulletin at a time. Its flash bulletins start with the word Flash and list every code the new calibration addresses, often a dozen or more. That is why 426 of its 501 bulletins count as software, and why every share on this page is also given without it.

Ford, Nissan, Hyundai, Kia and Subaru say so plainly. Ford summaries typically end with a sentence such as "This may be due to the software level of the PCM," Hyundai's with "software update," Subaru's with "availability of reprogramming files." The rule catches them reliably, which is part of why their shares are high.

GM's low share looks real. GM summaries often say only that a bulletin "provides repair information," so we checked the rule against them by hand. In 15 randomly chosen GM bulletins the rule did not flag, none clearly described a software update; 9 named a physical repair, such as camshaft position actuators, a charge air cooler outlet that disconnects, a PCV test before a camshaft cover, fuel components contaminated with debris, or a whole engine for a broken crank sprocket, and 6 did not state the remedy.

Honda's share is probably understated a little. In 15 unflagged Honda bulletins, one plainly said to "Update the PGM-FI software" (A22-045, for P0420), wording our rule does not match, and one more, B17-019, blamed PCM software misreading sensor inputs without naming the remedy. The rest were hardware: five of Honda's 2026 bulletins on reduced cylinder head gasket effectiveness with misfire codes, a thermostat whose inner seal detaches, fuel pump impellers that swell, faulty injectors and carbon on intake valves.

Finding 8: when a software flag is not a repair

Counting software bulletins is useful only if the software actually fixes something. Reading the flagged bulletins code by code turned up three kinds that do not, and a reader should know about them before quoting the shares.

Software that changes how a code is stored. Nissan NTB20-015 and Infiniti ITB20-007, for P0087 low fuel rail pressure, tell technicians to diagnose and repair first and then reprogram the engine computer, and state that "The ECM reprogram in this Service Procedure is not a repair for the DTC, but instead updates the way the permanent DTC is stored and allowed to be erased." Our rule counts both as software.

Software that adds a warning. GM's service updates N252510320 and N252510321, for P0016, reprogram the engine computer to "add to the existing Check Engine Light a Driver Information Center (DIC) warning message if DTC P0016 sets." The fault behind the code is untouched; the driver simply learns about it more clearly, in some cases over the air.

Software paired with parts. Ford TSB 19-2366 for the Police Interceptor Sedan 3.7L and TSB 19-2201 for the 2018-2019 Mustang 5.0L replace the catalytic converter and reprogram the PCM for P0420 and P0430; Infiniti ITB13-053A says to reprogram the ECM if needed and replace the exhaust manifold, three-way catalyst and air-fuel sensor on 2011-2012 QX56 models. They count as software, and the owner still gets a converter.

None of these is common enough to change the picture, but together they are the reason this page calls software a manufacturer remedy, not a guarantee that a code is harmless.

Code by code: what the bulletins actually say

Each profile gives the index figures and bulletins we read for that code, chosen at random outside Stellantis from software and non-software bulletins. Model years and build dates are quoted only where the bulletin summary states them. A note on what the quoted phrases are: every one is lifted word for word from the NHTSA summary of a numbered manufacturer document, and the document number printed beside it is enough to pull the same text from NHTSA's public file. This index carries no worked examples, no owner stories and no illustrative cases; where a figure appears it is a count or a median from the files named in the methodology, not a scenario written to make a point.

P0128, engine running cold. 125 bulletins from 13 manufacturer groups; software in at least 92, and 32 of the 62 outside Stellantis. Hyundai 19-01-016H is a pure logic change: an ECM "software update for DTC P0128 ... logic revision." Ford TSB 19-2116 says some 2016-2019 Fiestas built on or before 19 February 2019 set P0128 because of "PCM software parameters related to engine temperature," fixed by reprogramming. Kia ENG146 upgrades the ECM on some 2012-2013 Rio and Soul models for a list of codes including P0128. The hardware side is real too: Ford SSM 49407 and 49004 point 2020 Explorer and Aviator EcoBoost owners at the coolant temperature sensor or its wiring, Mazda 01-005-20 at a cylinder head temperature sensor that reads hot as cold, and Acura B17-048 at a thermostat whose inner seal detaches and holds it open. 110 NHTSA complaints name P0128, with a median of 67,650 miles in the 23 that give one. Full guide: P0128.

P0420, catalyst efficiency, bank 1. 143 bulletins from 12 groups; software in at least 86, and 31 of 85 outside Stellantis, where Ford alone has 39. Hyundai 5NP-F8N6C-10 updates the ECM "to prevent an increase in the catalyst temperature." Subaru 09-131-25 says P0420 "may become falsely detected due to unstable combustion caused by a downshift" and offers new reprogramming files. Ford TSB 21-2381 takes a different route on 2020-2021 Expedition and Navigator: high sulfur fuel, fixed by de-sulfating the converters. Honda A18-027 blames faulty injectors for "a false DTC P0420," and GM PIP5085 asks technicians for fuel flow data before replacing indirect injectors for P0420. The complaint file gives P0420 the highest median mileage in the index, 109,057 across 98 reports. Full guide: P0420.

P0430, catalyst efficiency, bank 2. 82 bulletins from 8 groups; software in at least 48, and 16 of 49 outside Stellantis. Ford's 2019 bulletins for the Police Interceptor Sedan and Mustang combine a new converter with a PCM reprogram. Ford program 14B05 gave Lincoln 2013-2014 MKS, MKT livery and Police Interceptor models an updated calibration "due to an accelerated catalyst degradation." GM 16NA111 checks the air box and air filter seal for P0420 and P0430, and Ford 20M01 covers driving maneuvers that can overheat the converter. P0420 and P0430 appear together in 24 complaints.

P0171, lean mixture, bank 1. 105 bulletins from 11 groups; software in at least 56, and 22 of 69 outside Stellantis. Ford TSB 25-2342, superseding 23-2195, says P0171 "may be due to the software level of the PCM." Toyota's side is mechanical: T-SB-0041-15 covers 2010-2013 Prius and 2012-2013 Prius V with a purge VSV/PCV line separated from the throttle body. GM PIP5686 points at an incorrectly installed or damaged foul air PCV tube, PIP4813B at the hydrocarbon absorber pad in the air cleaner lid, and service update N192273400 at a right-hand PCV tube that may not be fully seated. 102 complaints name P0171; 15 also name P0174. Full guide: P0171.

P0174, lean mixture, bank 2. 48 bulletins from 6 groups; software in at least 19, and 12 of 39 outside Stellantis. Nissan NTB19-030 and Infiniti ITB19-010 cover 2016-2018 Altima and QX60 V6 models with P0171, P0174, P2097 or P2099. Ford TSB 22-2393 reprograms some 2019-2021 F-150 5.0L trucks built on or before 4 March 2021. Toyota TSB000923 and Lexus LSB000523 cover 2014-2020 Toyota and 2013-2020 Lexus models with lean codes and low fuel pressure confirmed on a gauge, and Ford TSB 21-2106 fixes 2017-2021 Transit vans with a zip tie on a kinked vent line. Only 20 complaints name P0174, too few for a reliable median.

P0300, random misfire. 431 bulletins from 14 groups, the most in the index; software in at least 191, and 56 of 275 outside Stellantis. Ford SSM 49573 told dealers a calibration update was coming for 2021 F-150 PowerBoost trucks with rough idle and P0300. Honda A18-147 covers driveability issues with misfire codes or "a whirling noise coming from the engine compartment." The physical list is long: GM 18-NA-020 replaces a charge air cooler with moisture inside, Subaru 07-112-16R a new alternator for current output fluctuation, Ford SSM 47433 checks intake manifold runner control plates on 2015-2017 Mustang 5.0L, and GM PIE0505 asks the field for data on rough running with misfire codes. Honda and Acura add 20 distinct bulletins dated 2026 on reduced cylinder head gasket effectiveness, with overheating, coolant loss and P0300 through P0304, one of the largest single-condition clusters in the index. 365 complaints name P0300, and 94 also name P0301. Full guide: P0300.

P0301, cylinder 1 misfire. 276 bulletins from 12 groups; software in at least 114, but only 29 of 174 outside Stellantis. Ford TSB 24-2191 reprograms some 2024 F-150 PowerBoost trucks built on or before 14 May 2024, and TSB 18-2188 updates 2017-2018 F-Super Duty 6.2L trucks built on or before 2 May 2018 whose spark plugs foul in cold starts below 50°F. Land Rover LTB00799NAS1 blames "an on-board diagnostics (OBD) calibration error" with no hardware fault. Against that, Hyundai 5NP-B4B6V-06 replaces all four spark plugs, and Ford TSB 22-2017 covers a broken or binding right turbocharger turbine shaft on 2021 F-150 PowerBoost trucks built on or before 30 September 2021. Honda's P0301 list includes the five Soto piston ring extensions described below. 315 complaints name P0301.

P0456, very small evaporative leak. 269 bulletins from 11 groups; software in at least 194, but only 16 of 77 outside Stellantis, the steepest drop in the index. Kia ENG328 improves ECM logic for P0456 on some 2023 Sportage 2.5L models, and Ford TSB 21-2010 reprograms 2019-2020 Ranger. Outside software, Nissan NTB26-006 replaces a leaking fuel filler tube lower seal, Hyundai 20-01-020H deals with salt in the leak detection sensor of 2016-2019 Sonata Hybrids, and Mazda 01-005-19 says the concern is "most likely the result of the customer not getting the fuel cap completely closed."

P0455, large evaporative leak. 69 bulletins from 9 groups; software in at least 23, and 1 of 40 outside Stellantis: Ford TSB 21-2020, where 2020 Escape calibration was configured for the wrong fuel tank. Everything else outside Stellantis is hardware or procedure, from a fill level limit valve on the Sorento (Kia FUE033) to a vapor line disconnected inside the tank of the 2024 Edge (Ford 24-2199). Our separate reading of all 69 is in the P0455 guide.

P0442, small evaporative leak. 36 bulletins from 8 groups, none from Stellantis; our rule flags 1 as software, Volkswagen 01-23-03, and reading them all finds a second, 01-23-04. The rest are caps, filler pipes, chafed purge pipes such as GM's 17197 and PIP5461, canisters and leak test procedures such as GM's PIT4943. Our reading of all 36 is in the P0442 guide.

P0441, purge flow. 82 bulletins from 6 groups; software in at least 61, but 65 of the 82 are Stellantis, leaving 17, with 7 software. Hyundai 5NP-S5Y6V-04 is an ECM update for P0441 with "no vehicle performance concern," and a Volkswagen ECM update for low or no heat in cold weather is described as proactively repairing P0441 as well. Honda A23-091 and Acura B23-035 go the other way: variations in the purge control solenoid valve spring make it wear and stick.

P0401, EGR flow insufficient. 59 bulletins from 8 groups; software in at least 33, and 9 of 31 outside Stellantis. Ford TSB 19-2271 reprograms 2017-2019 F-Super Duty 6.7L diesels built on or before 9 January 2019. Toyota T-SB-0027-16 and Lexus L-SB-0015-16 trace P0401 on Prius models and the 2011-2012 CT 200h to "excess carbon build up at the valve assembly," with rough idle and a tapping noise at cold start. Volkswagen's P0401 guidance adds a smoke test and a cold air control valve test.

P0101, mass airflow range. 70 bulletins from 10 groups; software in at least 32, and 21 of 56 outside Stellantis, the highest share outside P0128. Infiniti's California emissions campaign reprograms the ECM on about 49,497 vehicles; Hyundai 21-01-041H revises P0101 logic on 2020 Elantra 2.0L. Mazda SA386 is a cautionary case: P0101 appearing "after PCM reprogramming due to a mislogic detection in the PCM calibration." GM PIP5446 looks for cast flashing near the mass airflow sensor, and Nissan NTB20-013 for ice inside the PCV hose of the Kicks below 14°F.

P0087, fuel rail pressure too low. 122 bulletins from 12 groups; software in at least 57, and 12 of 70 outside Stellantis. Nissan NTB19-048 reprograms 2019 Altima 2.5L models when the fuel level shows a quarter or less, and Audi ESA 24BX changes ECM software that could reduce fuel supply pressure. But the largest non-software group is Honda and Acura fuel pumps: A21-023 and B21-012 replace fuel pump motors whose impellers swell and seize, which can stop the engine while driving. The Nissan and Infiniti bulletins in Finding 8 show why a P0087 software flag needs reading. 180 complaints name P0087.

P0299, turbo underboost. 115 bulletins from 8 groups; software in at least 41, but only 7 of 71 outside Stellantis, the lowest share after P0442 and P0455. Ford TSB 20-2152 and 20-2246 reprogram 2019 Ranger and 2020 Explorer 2.3L. The physical side dominates: Ford TSB 19-2143 reconnects the charge air cooler outlet tube on 2011-2016 F-Super Duty 6.7L, GM PIP5651 the charge air cooler pipe at the throttle body, and Jaguar JTB00393NAS1 traces P0299 on 2.0L engines to "a breakdown of exhaust manifold internals." P0299 has the lowest median mileage among codes with enough data, 65,000.

P0016, crankshaft and camshaft correlation. 49 bulletins from 7 groups; software in at least 13, and 9 of 44 outside Stellantis, several of them GM's warning message updates in Finding 8. The rest is metal: GM PIP5102 checks whether the crankshaft reluctor has moved, PIP5855 replaces camshaft position actuator magnets, 17-NA-272 replaces the engine for a broken crank sprocket, and Land Rover LTB00916NAS5 covers a rattle with P0016 and P0017. 162 complaints name P0016, 42 of them with P0017.

P0011, intake camshaft timing. 70 bulletins from 12 groups; software in at least 18, and 7 of 59 outside Stellantis. Subaru 09-105-23 offers reprogramming for "rare cases" of P0011 and P0021, and GM service update N192266190 reprograms engines that run rough after an auto stop/start event. Hardware again leads: GM's A202304840 inspects a camshaft actuator oil control valve center bolt that can stick on 2020-2021 Buick Encore GX and 2021 Trailblazer, Ford SSM 49583 starts with the engine oil level on 2019-2020 F-150 5.0L, and GM 17-NA-098 replaces both camshaft position actuators. 107 complaints name P0011.

All 27 warranty extensions and emissions campaigns in the index

Finding 4 counts them; this is the full list, because for an owner the question is not how many exist but whether one covers their car. Terms are quoted only where the summary states them, and eligibility always depends on the VIN.

Catalyst codes, P0420 and P0430 (6)

• GM special coverage 15821: an exhaust leak where the bank 1 converter outlet meets the muffler inlet pipe sets P0420 with no other codes; covered for 8 years or 80,000 miles from the in-service date, with dealers replacing the exhaust pipe clamp.
• GM special coverage N232427150: a failed diesel particulate filter fuel injector sets P0420; dealers replace the injector "at no charge to the customer."
• Honda 18-022 and 18-023: the ECM misreads sensor inputs as warm-up converter deterioration and sets P0420 or P0430; two versions, one for most states and one for California, Connecticut, Maine, Massachusetts, New York and Vermont.
• Honda 20-100 and 21-010: PCM software may misinterpret sensor inputs as a deteriorated converter, and debris from the high pressure pump or injector machining can wear or clog injectors; P0420, P0430 and misfire codes.

Lean and airflow codes, P0171, P0174 and P0101 (5)

• GM special coverage 15317: a cracked PCV hose on some 2011 Cadillac CTS-V sets P0171 or P0174.
• GM special coverage 16139: a cracked air cleaner outlet duct sets P0171 or P0101.
• GM special coverages N202299080, N192210230 and N192291620: cracked PCV pressure regulator diaphragms in the camshaft cover of 1.4L and 1.6L engines, including 2014 Buick Encore, 2011-2014 Chevrolet Cruze, 2012-2014 Sonic and 2014 Trax under N202299080, and 2015-2016 Cruze and 2015 Sonic 1.4L under N192210230.

Misfire codes, P0300 and P0301 (8)

• Honda 13-078, 13-079, 13-080, 13-081 and 13-082: a powertrain warranty extension from the settlement of Soto et al. v. American Honda Motor Co., for piston rings that rotate and align and foul spark plugs, setting P0301 through P0304.
• Honda 18-147 and 19-012: driveability issues with misfire codes, P0172 or "a whirling noise coming from the engine compartment."
• Stellantis 09-002-14, X56 warranty extension: P0300, P0302, P0304 or P0306, with a cylinder leakage check and a cylinder head replacement if necessary.

Evaporative codes, P0442 and P0455 (2)

• Kia SC135: a voluntary emissions service campaign to inspect or replace the evaporative canister on some Optima, Optima Hybrid, Rondo and Sedona models in 28 salt belt states.
• GM emissions recall N192273600: 2016-2019 Chevrolet Volts whose purge pipe can chafe against an air conditioning hose connector and set P0442.

Fuel pressure, airflow and boost, P0087, P0101 and P0299 (6)

• Nissan and Infiniti California emissions campaigns: ECM reprograms on approximately 104,221 Nissan and 49,497 Infiniti vehicles registered in California, when a permanent code for P0448, P0101, P2008 or P0087 is recorded.
• Nissan NTB16-044: a voluntary emission service campaign reprogramming the ECM on certain 2015 Taxi vehicles for "improper calibration" that may cause poor idle and P0101, at no charge for parts or labor.
• GM emission recall N192271200: on 1.5L engines, the charge air cooler outlet duct can disconnect from the throttle body under boost, with reduced power and a check engine light.
• Nissan emission warranty extensions for the 2016 and 2017 Titan XD diesel: the turbo actuator and high-pressure turbocharger covered to 10 years or 150,000 miles.

The pattern is useful. Extensions cluster where a failure is expensive and the code is ambiguous: catalyst efficiency, misfires, and turbochargers. And several of them, Honda's catalyst extensions and the Nissan and Infiniti campaigns, pay for software, so a free update and a free repair can be the same visit.

Stellantis flash bulletins, examined

Every share on this page is given with and without Stellantis, so it is worth showing what its bulletins look like rather than only setting them aside.

We counted the distinct diagnostic trouble codes named in the summary of each of the 426 Stellantis bulletins our rule flags as software. The median bulletin names 7 codes, 164 name 10 or more, and one names 44. The 213 software bulletins from every other manufacturer name a median of 2 codes. A typical Stellantis summary reads "Flash: Powertrain Control Module (PCM) Updates. This bulletin involves reprogramming the PCM with the latest available software," followed by a list that can run from throttle position and crankshaft sensor codes to evaporative, oxygen sensor and thermostat rationality codes.

That has two consequences for anyone using the index. First, a Stellantis flash that names P0455 does not mean Stellantis found a large leak it could fix with software; it means the new calibration changes how, or whether, that monitor sets the code on those vehicles. Second, for owners of Chrysler, Dodge, Jeep, Ram, Fiat and Alfa Romeo vehicles, the practical advice is stronger, not weaker: before any parts for a code on that list, ask whether the powertrain control module is at the latest software level.

Some of these flashes are specific and say so. Jeep's 18-044-21 adds "Updated EVAP system diagnostics" for North America, and a group of 2019 Dodge bulletins tells technicians that if P0456 is present they should "use the wiTECH Small Leak Verification test (SLVT) to determine if a leak is present in the system" after the update.

Complaints, code by code

The index columns from NHTSA's complaint file, in one place. Complaint counts are owner reports naming the exact code in the description; mileage is the odometer the owner gave, where one was given.

The number in brackets is how many complaints gave a mileage. Towed is the share of complaints for that code where the owner said the vehicle was towed.

Three things stand out. Complaint volume and bulletin volume do not track each other. P0016 has 162 complaints but only 49 bulletins, while P0456 has 269 bulletins and 133 complaints; owners complain about what strands them, manufacturers publish about what they can fix. P0087 has the highest tow share among codes with more than 100 complaints, 3.9 percent, which fits the Honda and Acura fuel pump bulletins in its profile. Catalyst codes arrive late: P0420's median of 109,057 miles is the highest in the table.

How to find and read a bulletin for your own car

Everything in this index comes from a public file, and the same documents are available for any VIN.

Where to look. NHTSA's recall lookup at nhtsa.gov/recalls takes a VIN for open safety recalls. For bulletins, search NHTSA's vehicle page for your make, model and year and open the manufacturer communications list; each entry shows the summary we used and, for many, the full PDF. Manufacturer owner sites list recalls and many emissions campaigns by VIN. A dealer can see open campaigns and software levels for a VIN directly.

What the document types mean. The labels differ by company, and they matter:

• Technical service bulletin, TSB or SB: a repair procedure for a known condition, usually with parts, labor time and warranty information.
• Preliminary information, PI, PIP, PIC or PIT at GM: an early note to technicians, sometimes a fix, sometimes a request for data; GM's PIE engineering information bulletins ask dealers to send parts or measurements while engineering looks for a root cause.
• Special service message, SSM at Ford: guidance on a concern, often before or instead of a full TSB.
• STAR case at Stellantis: a record of past cases that, in its own words, "does not authorize warranty repairs."
• Special coverage or warranty extension: extra warranty for a named condition, with its own years or miles.
• Emissions campaign or emissions recall: a manufacturer-run repair for an emissions-related condition, free of charge.

How to read the summary. Look for four things: the vehicles, often with a build date cut-off such as "built on or before"; the codes; the cause, usually in a sentence beginning "This may be due to"; and the remedy, a reprogram, a part or a procedure. If the summary has no remedy, open the PDF.

What to say at the counter. Name the bulletin number, not the code: "My VIN falls under Ford TSB 25-2342 for P0171; is the PCM at the software level it specifies?" A bulletin does not oblige a dealer to repair for free unless it is a recall, campaign or coverage, or the car is under warranty, but it changes the conversation from guessing to a documented procedure.

Finding 9: what your brand's bulletins say, code by code

The overall shares hide how differently each manufacturer handles the same code. These are the counts for the five largest groups outside Stellantis; a bulletin that names several codes counts once under each.

Ford and Lincoln, 217 bulletins. Ford publishes most on misfires, 74 bulletins naming P0300 and 65 naming P0301, but only 23 and 12 of those are software. Its catalyst bulletins lean the other way: 20 of 39 for P0420 and 13 of 27 for P0430 are software, often paired with a converter, as in the Mustang and Police Interceptor examples above. Lean codes sit in between, 8 of 15 for P0171 and 5 of 13 for P0174, and P0128 is 5 of 10. Ford's boost, fuel pressure and timing bulletins are almost all hardware: 2 of 20 for P0299, none of 9 for P0087, 1 of 13 for P0011 and 1 of 11 for P0016. For a Ford owner: catalyst, lean and cold-engine codes justify asking about a PCM software level first; misfire, boost and timing codes usually do not.

GM, 206 bulletins. GM names P0300 in 70 bulletins, P0299 in 31, P0171 in 29, P0011 in 25, P0101 in 22 and P0016 in 21, and its software counts are small everywhere: 4 for P0300, 3 for P0011, 4 for P0016 including the warning message updates, 1 for each of P0299, P0171, P0101, P0420 and P0128. Our hand check found no hidden software among GM's unflagged bulletins. What GM publishes instead is inspection and parts guidance, from charge air cooler connections and PCV tubes to camshaft actuators and crankshaft reluctors, plus special coverages. For a GM owner: ask about special coverage and a Preliminary Information match for the code before assuming an update.

Hyundai and Kia, 105 bulletins together. The two brands share engines and a publishing style, and their software shares are high for the codes that are really logic: 10 of 16 Hyundai and 9 of 11 Kia bulletins for P0128, all 3 for P0441 in each brand, 3 of 3 Hyundai for P0171. Their evaporative leak bulletins are the exception: 5 of 17 Hyundai and 5 of 14 Kia for P0456, and none for P0455 or P0442, where the fixes are canisters, valves and the salt-damaged leak sensor on Sonata Hybrids. Kia's misfire bulletins are mostly software, 6 of 8 for P0300 and 5 of 6 for P0301. For a Hyundai or Kia owner: a thermostat or purge flow code is a strong case for an ECM update check; a leak code is not.

Nissan and Infiniti, 69 bulletins. Nissan has the most P0101 bulletins in the index, 23, and 15 of them are software, including the California emissions campaigns. It is also high on P0087, 10 of 11, and on misfires, 9 of 10 for P0300, but Finding 8 applies: some P0087 reprograms change how the permanent code is stored rather than repairing low fuel pressure. Its leak codes, P0456, P0455 and P0442, have no software bulletins at all. For a Nissan owner: its bulletins usually begin "IF YOU CONFIRM"; match the exact conditions before accepting either an update or a part.

Honda and Acura, 90 bulletins. Honda is the most hardware-heavy large group: 2 of 42 for P0300, 2 of 27 for P0301, none of 20 for P0087 and 2 of 10 for P0430, with an understatement of perhaps one or two bulletins in the fifteen we read by hand. Its misfire bulletins include the Soto piston ring extension and 20 bulletins dated 2026 on reduced cylinder head gasket effectiveness, and its P0087 bulletins are fuel pump impellers. For a Honda owner: a misfire or fuel pressure code is far more likely to be a part or a warranty extension than an update, which makes a VIN check for extensions the first step.

Questions this index cannot answer yet

How often each fix works. Bulletins describe a remedy, not its success rate. A software bulletin that fixes most cars and one that fixes few look the same in the file.

How many vehicles each bulletin covers. Unlike recalls, bulletins rarely state a population. We report bulletins, not cars, and a single bulletin can cover one trim or a whole platform.

The share of each code that is software in the real fleet. For that, we would need repair orders, which are not public. The index shows how often manufacturers chose software as a documented remedy, which is a different and narrower measure.

Remedy types other than software. We tried to classify replacements, inspections and procedures from summaries and stopped when a hand check came out at about three correct in four. The per-location readings in our P0442 and P0455 guides were done by hand for that reason, one document at a time.

Codes outside the 17. P0172, P0175, P0446 and the bank 2 camshaft codes are all in NHTSA's file. We started with the 17 most searched and most common in our guides, and the method file is written so the same rules run on any code.

How the index will be updated

We plan to rerun the same rules when a new quarter of bulletins is available, publish the new CSVs alongside the old ones, and note any rule change in the method file with its date. A correction that changes a published share will be listed on this page with its reason.

How to use this if your check engine light is on

Get the exact code, not the category. A free scan gives you the code; this index is keyed to it.

For P0128 and the catalyst and lean codes, ask about updates before parts. Ask the dealer to check your VIN for technical service bulletins and pending software updates. Updates on emissions-related systems are often done at no cost when a bulletin or campaign applies, but that depends on the bulletin and your warranty.

For leak, timing, boost, fuel-pressure and misfire codes, insist on a test. A smoke test, a fuel pressure reading, a compression or leak-down test. The bulletins for these codes are mostly about parts and procedures.

Listen as well as read. Misfires, timing chain rattle and failing fuel pumps often make themselves heard before or alongside a code; our study of car noises that come with no warning light found that most owners who describe a noise report no warning at all.

Free, no card, no subscription. The report comes by email.

What this index does not show

It is not a failure rate or a reliability ranking. A bulletin is a manufacturer communication. Makers publish at different rates and in different formats; Stellantis alone accounts for 501 of the 1,412 bulletins.

It does not say a software update will fix your car. Bulletins apply to specific vehicles and conditions, and many combine software with inspection or parts.

The software share is a floor. It is read from NHTSA's summary of each bulletin, not the full document. In our check of unflagged bulletins, about one in three summaries did not say what the repair was.

Other remedy types are not reported. A hand check of our replacement and inspection labels put them at roughly three correct in four, too low to publish.

Complaint numbers are small for some codes and are unverified owner reports.

Methodology

Source. NHTSA's manufacturer communication flat files TSBS_RECEIVED_2015-2019, TSBS_RECEIVED_2020-2024 and TSBS_RECEIVED_2025-2026, downloaded in September 2026, using the document ID, communication date, make, model, model year and summary fields. Latest communication date in the index: 31 August 2026.

Inclusion. The summary names the code as a whole word. Removed before counting: heavy-truck, bus, motorcycle and RV makers; 205 helpline analysis entries and documents marked not applicable to US-market vehicles; 138 Honda and Acura dealer messages, parts-collection requests and owner notification letters, which announce, investigate or repeat a numbered bulletin rather than describe a repair; and 11 entries with no document number.

One bulletin, counted once. A bulletin is one manufacturer group plus one normalized document ID. Brands of the same group share IDs (Buick, Cadillac, Chevrolet and GMC; Chrysler, Dodge, Jeep and Ram), and revision and version marks such as REV A, a trailing letter or a Volkswagen _2 suffix are removed, so PIP5110, PIP5110A, PIP5110B and PIP5110C count once. That leaves 2,151 code-bulletin pairs and 1,412 distinct bulletins.

Software rule and audits. The exact pattern, the excluded makers and the grouping rules are in the published method file. Of 30 randomly selected flagged bulletins, 28 were plainly software updates and 2 made reprogramming conditional. Of 40 randomly selected unflagged bulletins, 2 were clearly software updates and 14 did not state a remedy.

Manufacturer audits. Because summary styles differ, we repeated the unflagged check by manufacturer for the two largest groups with low shares. Of 15 randomly chosen unflagged GM bulletins, 0 clearly described software, 9 named a physical repair and 6 stated no remedy. Of 15 unflagged Honda and Acura bulletins, 1 clearly described software, 1 blamed software without naming the remedy, and 13 were hardware or unstated.

Periods. Finding 6 assigns each bulletin to the period of its latest communication date in NHTSA's file. A bulletin first issued in 2016 and revised in 2025 therefore counts in 2025-2026. The last period covers January 2025 to August 2026. The first period is labeled "through 2019" because NHTSA's 2015-2019 file also holds 119 bulletins whose latest version is dated before 2015; they were received or indexed from 2015 on, so they stay in the index and are counted in the first period, both in the table and in the per-code figures.

Code profiles. For each code we drew bulletins at random from outside Stellantis, separately from the software and non-software groups, read their summaries and quoted only what the summaries say. Where a model year or build date appears in a profile, it is taken from the summary text, not from NHTSA's product list, which often attaches a bulletin to a wider range of years than the document covers.

Stellantis code counts. The Stellantis section counts distinct codes matching the OBD-II pattern (a letter P, U or C followed by four hexadecimal characters) in each summary. Codes written in ranges, such as P0301-P0306, count as the codes actually printed.

Complaints. 777,040 distinct vehicle complaints received by NHTSA from 1 January 2015 to 8 September 2026, matched on the exact code in the complaint text.

Download the data

• Index summary, one row per code (CSV)
• All 1,412 bulletins with document IDs, dates, model years and flags (CSV)
• Exact rules, exclusions and audit notes (TXT)

License. CC BY 4.0. Please credit PulsCar Check Engine Code Index and link to this page.

For reporters. If you need a cut we did not publish, one manufacturer, one model year band, or a code not in the 17, email [email protected] and we will run it with the same rules.

Code guides

The table of 63 guides near the top of this page links each guide with its meaning. For the light itself, start with check engine light on.

Sources and documents

Primary sources only.

1. NHTSA manufacturer communication flat files — received 2015 to 2026, with field dictionary. Field dictionary
2. NHTSA ODI complaint flat files — 777,040 distinct vehicle complaints, 1 January 2015 to 8 September 2026. Field dictionary
3. Ford TSB 25-2486 — PCM software, P0128. NHTSA summary in the bulletin file.
4. Mitsubishi SC-26-003 — ECU reflash for P0128, P2096 and P050A. NHTSA summary in the bulletin file.
5. GM 22-NA-054, March 2022 — 2021 calibration, P0128. PDF
6. GM special coverage N252508350, 21 October 2025 — thermostat, 15 years or 150,000 miles. PDF
7. GM 18-NA-331, November 2018 — ECM reprogram, P0420. PDF
8. Ford TSB 25-2188, May 2025 — Explorer 2.3L PCM software, P0420. PDF
9. Ford TSB 23-2195 and 25-2342 — F-150 3.3L PCM software, P0171. 23-2195 · 25-2342
10. Honda SB 20-100, November 2020 — 2016 Pilot, software and injectors, 10 years or 150,000 miles. PDF
11. Honda SB 18-022 and 18-023, June 2018 — Accord Hybrid catalyst warranty extension, P0420 and P0430. NHTSA summary in the bulletin file.
12. GM special coverage 15821, 2016 — exhaust clamp, P0420, 8 years or 80,000 miles. NHTSA summary in the bulletin file.
13. GM special coverage N202299080, July 2020 — camshaft cover and PCV, about 810,404 vehicles, 10 years or 120,000 miles. PDF
14. Ford TSB 25-2133 and Volkswagen 01-21-02 — software bulletins the rule does not flag. 25-2133 · 01-21-02
15. PulsCar index files — summary, bulletin list, method and audits. Method
16. SAE J2012, Diagnostic Trouble Code Definitions, April 2002 edition — code format, ISO/SAE and manufacturer controlled ranges, powertrain groups; scanned copy of the edition incorporated by reference in federal rules. PDF
17. 40 CFR 86.1 — incorporation by reference; lists SAE J2012 Revised April 2002 as incorporated by reference. eCFR

How these numbers were built: one script over NHTSA's public bulletin and complaint files, run on 17 September 2026, with the inclusion rules, grouping, software pattern, audits and limits described above and in the published method file.

Prices verified: not applicable, this index quotes no repair prices · Technical documents verified: 17 September 2026 · Data refreshed: 17 September 2026 · Code format and guide list verified: 7 October 2026

Re-ran the rules and got a different number? Email [email protected] with your counts and file dates.