P0174 Code in 2026: Lean on Bank 2, and Whether It's One Side or Both

P0174 is half of a pair, and the other half decides most of what happens next.

On a V6 or V8, the engine has two rows of cylinders, called banks, and the computer trims the fuel for each one separately using an oxygen or air-fuel sensor in that bank's exhaust. P0174 — "System Too Lean, Bank 2" — means the computer has been adding fuel to bank 2 to correct a lean mixture and has reached the limit of what it is allowed to add. It says there is more air than fuel on that side. It does not say whether the extra is air getting in where it should not, fuel that is not arriving, or a sensor or calibration that has the numbers wrong.

We read every complaint in NHTSA's federal file that names P0174 — 25 of them, after one false match was set aside — and went through every manufacturer communication record that names it: 84 records, which collapse into 38 distinct documents once revisions, supersessions and one Acura dealer message filed sixteen times are grouped. Two findings shape this article. Twenty of the 25 complaints also name P0171, the same code for bank 1, which means the cause sat upstream of both banks. And only four documents deal with P0174 on its own — a Nissan and an Infiniti reprogram, a Ram fuel line bundle and a GM repair tip — while most of the rest describe PCV hoses, intake boots, software and fuel.

By the end you will know whether your P0174 is a one-bank or a both-bank case, which of five routes it is on, what each costs in 2026, which bulletin or warranty may pay, and the cheap cause that gets skipped when a sensor is quoted first.

Claims marked 🟢 rest on a bulletin, program or recall listed in the Sources section. Claims marked ⚪ are shop-price estimates carried from our repair guides. The count of bulletins that name P0174 by our Check Engine Code Index method is cited from that index, not recomputed here; our own grouping into documents is published separately.

I built PulsCar after a $380 "full diagnostic" in Phuket in 2025 led to roughly $6,000 over six months across several shops, and the sound never went away (the story is on the About page). A lean code is exactly the kind that invites a parts cannon — a sensor, then another sensor — so every claim below that rests on a document says which one.

One bank or both: the first thing P0174 tells you

Every route in this guide starts from one question: is P0174 alone, or is P0171 stored with it?

Both banks breathe through the same air filter, the same airflow sensor and the same intake plenum. They drink from the same fuel pump and the same tank. So when both are lean at once, the cause is almost always something they share: air entering after the airflow sensor, an airflow sensor reading low, a PCV system leaking into the intake, fuel pressure falling, or fuel the computer has misjudged. That is the case in 20 of the 25 federal complaints.

When bank 2 is lean on its own, the list narrows to things that feed or measure only that side: an intake gasket or vacuum port on that side, a PCV tube routed to that side, an exhaust leak ahead of that bank's upstream sensor that lets outside air into the reading, a restricted injector or fuel feed to that bank, the bank 2 air-fuel sensor itself when its own code is stored — and, on some engines, software.

The rule that saves money: with P0171 and P0174 together, test the shared systems before replacing anything that belongs to one bank. With P0174 alone, look at what belongs to bank 2 first — and check whether your engine has a document for it, because four do.

First: is this really P0174? The lean and fuel codes side by side

What matters most here: P0174 with P0171 and nothing else points at air or fuel shared by both banks. P0174 with P0101 or P0102 points at the airflow sensor or the air path around it. P0174 with P0087 or a hard start points at fuel pressure. P0174 with P0496 or a purge code points at the EVAP system. P0174 alone, on a V8 truck or SUV, is worth a bulletin search before anyone reaches for a part.

Which side is bank 2 on your engine

Bank 1 is the bank that contains cylinder 1; bank 2 is the other one. Which physical side that is depends on the engine, and it is not the same across manufacturers, or even across one manufacturer's engines.

Where the documents name it. 🟢 Honda's dealer message for 2016-2020 Acura MDX, RDX and TLX models names the codes by position: "P0171 & P0174 (Rear/Front Bank Fuel System Too Lean)" — on those transverse V6 engines, bank 2 is the front bank, toward the front of the car. 🟢 GM's PIP5341, for 2007-2016 full-size V8 trucks and SUVs, sends the technician to "the positive crankcase ventilation tube for a vacuum leak on the left side of the engine," and GM's service update N192273400 for 2020 light-duty Silverado and Sierra pickups names the "right-hand side" PCV tube — useful as a reminder that a leak on one side can still set both codes on some engines, because the PCV system feeds the shared intake.

Everywhere else, the service manual's cylinder numbering diagram is the answer, and a shop can show it in a minute. It matters because the parts that belong to bank 2 — its upstream air-fuel or oxygen sensor, its intake gasket, its exhaust manifold — are different parts from bank 1's, often at different prices and different depths in the engine bay. A rear-bank part on a transverse V6 can be hours deeper than the front one.

The practical rule. Before approving any one-bank repair for P0174, ask the shop which side of the engine is bank 2 and why the part they want to replace is on it.

Fuel trim in plain English, and the test that splits air from fuel

The computer measures the air coming in, calculates how much fuel should go with it, and then checks its work with the sensor in each bank's exhaust. If the exhaust shows more oxygen than expected, the mixture is lean, and the computer adds fuel. The quick correction is short-term fuel trim; the learned correction that carries over from drive to drive is long-term fuel trim. Both are shown as a percentage. A positive number means the computer is adding fuel.

P0174 sets when bank 2's correction reaches the manufacturer's limit and stays there. The limit varies by engine, which is why the documents describe the evidence rather than a number: 🟢 Toyota's pump bulletin describes "positive fuel trims including a no pressure condition verified by a manual fuel pressure gauge," and its flex-fuel bulletin for the Tundra and Sequoia describes the opposite, "negative fuel trims and an elevated alcohol density estimate" — a computer that believes it is burning more ethanol than it is.

The test that splits air from fuel. Our P0171 guide describes it in detail, and it works the same way for bank 2. Read the fuel trims at a warm idle, then at a steady 2,500 rpm in park.

• Trims high at idle, near normal at 2,500 rpm: unmetered air. A fixed leak matters less as airflow rises, so a vacuum or PCV leak shows up at idle and fades with revs.
• Trims high at both, or worse under load: fuel supply or an airflow sensor reading low. A weak pump, a restricted filter or line, or a sensor under-reporting air all get worse as demand rises.
• Bank 2 high, bank 1 normal: something that belongs to bank 2.
• Both banks high by similar amounts: something they share.

Any scan tool that shows live data can do this. It costs nothing, and it decides which half of the rest of this guide applies.

The 10-minute P0174 check

1. Read every code, and write down whether P0171, P0101, P0087, P0300-P0308, P2096-P2099 or an EVAP code is also stored.
2. Check the oil filler cap and the dipstick. A loose cap or an unseated dipstick is an air leak into the crankcase, and from there into the intake through the PCV system. 🟢 GM's 21-NA-105 lists both among its visual checks.
3. Look at the intake duct between the air filter box and the throttle body. Squeeze it along its length; a crack often hides in a fold. 🟢 GM's 22-NA-171 is about exactly that on the 3.6L Colorado and Canyon.
4. Check the air filter box clips and the airflow sensor connector.
5. Listen at idle with the hood up for a hiss or whistle. 🟢 GM's service update N192273400 describes "a whistling sound" from an unseated PCV tube; Stellantis's 09-025-25 describes a "hissing noise from the engine" from a disconnected purge line.
6. Note when the light came on — after a fill-up, after a battery change, after a repair, in cold weather, on a long climb.
7. If you have a scan tool with live data, do the idle and 2,500 rpm fuel trim comparison above.
8. Run the VIN at nhtsa.gov/recalls and on the manufacturer's owner site, and ask a dealer to check for open campaigns and bulletins.

Eight P0174 situations, and which is yours

"P0171 and P0174 together, engine runs fine." Shared cause, probably air. Route 1.

"P0174 alone on a 5.6L Nissan Armada, Titan, NV or an Infiniti QX80." A reprogram exists. Route 2.

"P0174 alone on a 2021 Ram 1500 5.7L with weak acceleration." A fuel line bundle, if built in the window. Route 3.

"Lean codes and a whistle from the engine on a GM truck." A PCV tube. Route 1, and the PCV section.

"Lean codes after filling up, or a hard start after refuelling." Fuel or EVAP. Route 3, and the Toyota section.

"Lean codes on a flex-fuel F-150, Tundra or Sequoia." The computer may have mislearned the ethanol content. Route 2 and the flex-fuel section.

"Lean codes on a nearly new truck." 🟢 GM's 21-NA-105 describes lean codes on 2020-2021 Colorado and Canyon trucks "usually under 1800 miles." Route 2.

"Somebody replaced a sensor and the code came back." Route 4, and the traps.

The P0174 price ladder, from the bottom up

Read it from the bottom up: the expensive lines are the ones a P0174 most often does not need. What moves a car between them is whether P0171 is also stored, a fuel trim reading at two engine speeds, a smoke test and a VIN lookup.

How much does it cost to fix a P0174 code? Most P0174 repairs cost less than the sensor people buy first. Our repair guides carry $60 to $150 for a smoke test, $50 to $150 for a fuel pressure test, $110 to $220 for a PCV valve and $15 to $40 in parts for a cracked intake duct or split hose, while an air-fuel sensor runs $200 to $500 and an intake manifold gasket $680 to $1,250. In PulsCar's reading of 38 manufacturer documents that name P0174, the most common fixes are software, PCV tubes and hoses, and fuel supply, and GM's 21-NA-105 covers its Colorado and Canyon reprogram for eight years or 80,000 miles. The owner in the federal file who reported a bill paid $523.80 for PCV and purge repairs on a 2007 Silverado that did not end the problem, which is the argument for measuring first.

The P0174 number, by what you drive

The vehicles that carry a document naming P0174, and what each document adds.

Full tables: 38 documents naming P0174 · the 25 complaints, read.

The five P0174 routes, cheapest first

Route 1 · Air the sensor never counted — PCV tubes, intake boots, purge lines — $0 to $300

The airflow sensor sits just after the air filter. Every bit of air that enters after it — through a cracked duct, a loose PCV tube, an unseated oil cap, a purge valve stuck open or a split vacuum line — reaches the cylinders without being counted, and the computer has to add fuel to make up for air it never measured. It is the story behind many P0174s, and GM's documents tell it again and again.

What the documents show. 🟢 GM's PIP5341 tells technicians working on 2007-2016 full-size V8 trucks and SUVs with a rough idle and P0171 or P0174 to "inspect the positive crankcase ventilation tube for a vacuum leak on the left side of the engine," replace it "and cover it with conduit to protect from repeat damage." 🟢 PIP5686A, for 2019-2020 Silverado and Sierra 1500 with the 5.3L, describes "a rough idle, lean running concern and/or air leak noise from the PCV system" caused by "an incorrectly installed foul air PCV tube or tube may be damaged," and its procedure is mostly hands: tug on both tube ends, press a loose one in "until it clicks," smoke-test, and look for damaged or missing O-rings before any new part. 🟢 Service update N192273400 for 2020 light-duty Silverado and Sierra pickups says the right-hand PCV tube "may not be fully seated (loose)," that customers "may experience a whistling sound," and that "Disconnection of this line is monitored through the fuel trim diagnostics"; the fix needs no parts and 0.2 hours, and the update itself expired with each truck's new-vehicle warranty. 🟢 GM's special coverage 15317 replaced a PCV hose that "may crack" on the 2011 Cadillac CTS-V. 🟢 22-NA-171, for 2017-2022 Colorado and Canyon with the 3.6L, blames a "possible cracked/failed rubber intake boot" and replaces the air cleaner outlet duct, with a note that is easy to miss: "Do Not to remove engine cover when performing leak check." And 🟢 Stellantis's 09-025-25 covers a "Disconnected Purge Line" on 2025 Wagoneer, Grand Wagoneer and Ram 1500 models with the 3.0L Hurricane HO built from September 2024 to June 2025, where a "Quick connect latch has diminished retention after installation," with P0171, P0174 and misfires and a "Hissing noise from the engine."

What the owners report. A 2007 Silverado owner's dealer ran a smoke test on the EVAP and induction systems and "found leaks at the PCV hose, purge valve hoses and purge valve is stuck open." All three were replaced for $523.80, and the owner writes that the problem was "still not fixed" — the truck's main complaint was a clicking no-start, which a lean code does not explain. A 2013 GMC Terrain's dealer found P0496, the code for purge flow when there should be none, alongside P0171 and P0174. A leak can be real and still not be the only thing wrong.

The cheap cause that gets skipped. The oil filler cap and the dipstick. The crankcase is connected to the intake through the PCV system, so a cap that is not tightened, a cracked filler neck or a dipstick not pushed fully home is an air leak into the intake. 🟢 GM's 21-NA-105 lists "PCV hoses and oil separator connections loose or not completely snapped on," "Oil filler caps loose," "Oil filler adapter cracked" and "Oil level sensor (dipstick) not fully seated" as its first checks. None of them costs anything to look at.

Fix it yourself — the honest split. Reseating a PCV tube, replacing a cracked intake duct, tightening an oil cap and pushing a dipstick home are driveway jobs. Finding a leak you cannot hear needs a smoke machine, and ⚪ our guides carry $60-$150 for the test. Pay for the smoke test before paying for any part that sits downstream of it.

At the shop — say this: "Both banks are lean. Before any sensor, can you smoke-test the intake, PCV and EVAP systems and check the fuel trims at idle and at 2,500 rpm? I'd like to know whether it's air or fuel."

Route 2 · Software and relearns — the documents that fix it with a laptop — $0 to $200

Fifteen of the 38 documents we grouped are software updates, and several of them are the clearest answers in the file. Our Check Engine Code Index, which counts bulletins by a different method, puts software in at least 19 of 48 bulletins naming P0174, and 12 of 39 once Stellantis, which issues many flash bulletins each listing dozens of codes, is set aside. We cite those figures rather than recompute them.

The P0174-alone reprograms. 🟢 Nissan's NTB20-009A, June 2021, applies to 2017-2019 Armada, 2017-2021 NV cargo and passenger vans and 2017-2019 Titan and Titan XD with the 5.6L VK56VD, when "The MIL is ON and only DTC P0174 (FUEL SYS LEAN B2) is stored in the ECM." The technician confirms the engine computer's part number against a table; "If it does not match one of the part numbers in Table 1, this bulletin does not apply." 🟢 Infiniti's ITB20-005, February 2020, does the same for the 2016-2019 QX80 and adds that, after the reprogram, the technician performs throttle valve closed position, idle air volume learning and accelerator closed position procedures, preceded by a ten-minute drive to reach them.

The Colorado and Canyon. 🟢 GM's 21-NA-105, May 2021, for 2020-2021 Colorado and Canyon with the 3.6L built up to 1 May 2021, says lean codes have set on "very low mileage vehicles, usually under 1800 miles," that "The cause of the condition may be software anomalies," and that after a visual check of the PCV and oil filler items the technician should reprogram "Whether you find any concerns or not." It also states that "ECM reprogramming is covered for 8 years/80,000 miles (U.S.)." On a 2021 truck, that window runs into 2029.

The F-150. 🟢 Ford has issued four reprogramming bulletins for the 5.0L that name lean codes: TSB 21-2443 for 2019-2020 flex-fuel trucks, and 21-2083, 21-2154 and 22-2393, first for 2021 trucks and then for 2019-2021 trucks built on or before early March 2021, which cite "various software parameters within the PCM" and require a keep-alive memory reset. 🟢 For the 2018 2.7L EcoBoost, TSB 20-2324 attributes lean, rich and misfire codes to "software in the powertrain control module (PCM) or direct injection fuel injectors leaking down"; where the injectors are at fault, its parts list is all six plus the high-pressure fuel tubes.

The rest. 🟢 Nissan's NTB19-030 and Infiniti's ITB19-010 reprogram the engine computer, when its part number is listed, on VQ35 engines in the 2016-2018 Altima, Maxima, Murano, Pathfinder and QX60 with P0171, P0174, P2097 or P2099 — 2018 models only up to build dates between February and July 2018. 🟢 Infiniti ITB15004 reprograms the 2014-2015 Q50 when the light comes on "after the engine has been idling a while" with P0171 and/or P0174. 🟢 Chrysler's 18-057-16 and two later flashes cover the 2017 Pacifica 3.6L; Ram's 18-050-21 and 1814522 the 2021 Ram 1500; Jeep's 21-029-16 and 1810723 the 2014 and 2021 Grand Cherokee.

Why does P0174 set on only one bank? Because something affects that side alone, and on some engines that something is software. In PulsCar's reading of the 84 manufacturer records naming P0174, only four documents deal with P0174 by itself: Nissan's NTB20-009A and Infiniti's ITB20-005 reprogram the engine computer on 5.6L Armada, Titan, NV and QX80 models when only P0174 is stored; Ram's 14-005-21 replaces a blocked fuel and EVAP line bundle on 2021 Ram 1500 5.7L trucks built in autumn 2020; and GM's PIP5187 swaps back a fuel rail after a cylinder head replacement. Outside those, one-bank causes are physical: an intake gasket or vacuum port on that side, an exhaust leak ahead of that bank's upstream sensor, or the bank 2 air-fuel sensor when its own code is stored. Ask for a bulletin search before any part is replaced.

The cheap cause that gets skipped. The part-number check. Every Nissan and Infiniti reprogram above hinges on the step "confirm the current ECM part number" — a two-minute check that decides whether a free fix exists. A shop that does not have the manufacturer's tool cannot do it, which is the one case where a dealer visit for a scan is worth paying for.

At the shop — say this: "Only P0174 is stored. Can you check the engine computer's part number against NTB20-009A, and is there any other reprogram or campaign on this VIN before we talk about parts?"

Route 3 · Fuel supply — pump, lines, filter, ethanol — $50 to $1,500

When the fuel supply falls short, both banks go lean together, and the code often comes with a hard start or hesitation under load. The documents name pumps, a line bundle, a filter and the fuel itself.

What the documents show. 🟢 Toyota's T-SB-0009-23 covers 2014-2020 Toyota models from the Camry and RAV4 to the Tundra, and Lexus's LSB000523 2013-2020 Lexus models, with "a hard start and/or MIL ON condition" and P0171, P0174 or P0087, where "Techstream data list analysis may reveal positive fuel trims including a no pressure condition verified by a manual fuel pressure gauge." The fix is a pump, under the powertrain warranty — a window that has closed for most of those cars, which is why the recalls matter more: 🟢 20V-012 and 20V-682 replaced the in-tank pump on a long list of 2013-2020 Toyota and Lexus models, as our P0087 guide sets out. 🟢 Ram's 14-005-21, for 2021 Ram 1500s with the 5.7L Hemi built between 21 August and 2 October 2020, describes a "Fuel Line Blockage" with P0174 alone, reduced acceleration and rough starting, and replaces "the engine fuel/EVAP forward line bundle." 🟢 Land Rover's SWA09013 describes in-line fuel filters on 2002-2005 Freelanders that may contain "an uncontrolled amount of adhesive," restricting flow, with lean and misfire codes possible.

What the owners report. Five of the 25 federal complaints naming P0174 are Toyotas, and all five describe fuel. A 2008 Tacoma stalled climbing the Houston Ship Channel bridge at 60 mph with P0171 and P0174; the fuel pressure was checked several times before an intermittent drop below 20 psi was finally seen, the pump and strainer were replaced, and the owner reports no light in more than 400 miles. A 2020 Avalon owner describes hard starts that began after a fill-up and a stall pulling away from the pump, and writes that the VIN is not on the pump recall they found. The Highlander complaints are in their own section below.

The cheap cause that gets skipped. The gauge. A fuel pressure test costs ⚪ $50-$150 in our guides and separates a supply problem from an air problem in minutes, and Toyota's bulletin requires the gauge reading before a pump is replaced. A pump bought on a lean code alone is a guess.

At the shop — say this: "Can you put a gauge on the fuel pressure, at idle and under load, and check this VIN for fuel pump recalls 20V-012 and 20V-682 and bulletin T-SB-0009-23 before quoting a pump?"

Route 4 · Sensors — the airflow sensor, and the air-fuel sensor not to buy first — $10 to $500

Two sensors sit on either side of the fuel calculation. The airflow sensor, before the engine, tells the computer how much air is coming in; if it under-reads, the computer under-fuels both banks. The upstream air-fuel or oxygen sensor in each bank's exhaust tells the computer how the mixture turned out; it is the sensor that reports the lean condition, and replacing it because it reported one is the classic wasted repair.

What the documents show about the airflow sensor. 🟢 GM's PIP5446, for 2006-2018 trucks, SUVs, Camaros, Corvettes and others with a harsh 1-2 and 2-3 shift, a sputter between 0 and 30 percent throttle and a rough idle, tells technicians to "inspect for cast flashing near the Mass Air Flow sensor" — a casting burr that disturbs the air the sensor reads. 🟢 PIP4813B, for 2010-2013 Camaros, points at a "hydrocarbon absorber pad that is on the inside of the air cleaner lid" that may come loose. Neither replaces the sensor.

What the documents show about the air-fuel sensor. 🟢 Nissan's NTB19-022 and Infiniti's ITB19-007, March 2019, cover the 2017-2018 Altima and 2017-2019 Armada, Sentra, Frontier, Versa Note, Titan, Rogue, NV and Murano, and several Infinitis. Their flow chart runs a confirmation drive — one minute at 3,500-4,000 rpm, a minute at idle, then twenty minutes at 2,500-3,000 rpm — and then branches: if P2096, P2097, P2098 or P2099 appears, replace the sensor; if not, "Do NOT replace the A/F sensor" and continue diagnosis "excluding A/F sensor." 🟢 The two related bulletins for VQ35 engines, Nissan's NTB19-030 and Infiniti's ITB19-010, sound like sensor bulletins — their titles list P0171, P0174, P2097 and P2099 — but read in full they are not: the technician runs the normal diagnosis, then checks the engine computer's part number against a table and reprograms it if listed. Only Infiniti's ITB11054A, for the 2011-2013 QX56 and M, replaces an air-fuel sensor, and only when the lean and misfire codes are traced to that sensor.

The cheap cause that gets skipped. A contaminated airflow sensor, or air bypassing it. ⚪ A can of sensor-specific cleaner is about $10 in our guides. A 2013 Traverse owner's dealer cleaned the airflow sensor for P0171 and P0174, and the codes did clear — though the stalling the owner reported did not, which is a reminder that a lean code and a stall can be two problems.

Fix it yourself — the honest split. Cleaning an airflow sensor with the right spray, checking its connector and inspecting the air box are driveway jobs. Replacing an upstream air-fuel sensor on the front bank of many V6s is too; on the rear bank it can mean removing the intake. Neither sensor should be bought until the evidence points at it.

At the shop — say this: "Is there a sensor code, P2096 to P2099 or a bank 2 heater or circuit code, stored with the P0174? If not, I'd like the leak and fuel checks done before the air-fuel sensor is replaced."

Route 5 · Injectors, carbon and the repair that caused it — $150 to $3,000

When the air is right and the pressure is right and bank 2 is still lean, the fuel may not be reaching bank 2's cylinders in the amount commanded: a restricted injector, deposits on a direct-injection engine, or a part installed incorrectly.

What the documents show. 🟢 GM's PIP5187, for 2010-2011 Equinox, Terrain, SRX, CTS and LaCrosse, describes a check engine light "after the Cylinder Head was replaced": if the technician finds P0174 and the replacement head came with injectors already installed, "replace the fuel rail with the original fuel rail off the car." It is one of the four documents about P0174 alone, and it is about a repair that set the code. 🟢 Ford's TSB 20-2324 names direct injectors "leaking down" on the 2018 F-150 2.7L as one of two causes, with software the other.

🟢 Honda's sixteen-times-repeated dealer message for 2016-2020 Acura MDX, RDX, TLX and RLX, covered below, is also an injector document: it wanted parts only when a misfire had been "traced to the fuel injectors," with lean codes optional.

What the owners report. A 2017 Kia Cadenza owner with the 3.3L writes that the dealer diagnosed "carbon buildup causing the fuel injectors to malfunction" after the car stalled in traffic, with P0171, P0174 and a fuel pressure code, P0191. A 2008 Buick Enclave owner lists a purge valve, canister, PCV valve and breather hoses, throttle body, plugs, coils, intake gaskets and oxygen sensors replaced — and lean codes still present. That list is the cost of skipping the measurements in Routes 1 and 3.

The cheap cause that gets skipped. ⚪ A fuel system cleaner or a professional injector service, at $10-$25 and $60-$150 in our injector guide, is worth trying on a port-injected engine before a flow test, and a flow test is worth paying for before a set of injectors.

At the shop — say this: "Can you do an injector balance or flow test on bank 2 before we replace injectors? And was any part of the fuel system disturbed in the last repair?"

P0174 alone: the four documents about one bank

Of 38 documents, five name P0174 without P0171, and in four of them P0174 is the only lean code:

1. 🟢 Nissan NTB20-009A — 2017-2019 Armada, 2017-2021 NV, 2017-2019 Titan and Titan XD, 5.6L VK56VD: reprogram if the engine computer part number is listed.
2. 🟢 Infiniti ITB20-005 — 2016-2019 QX80: the same, plus throttle and idle relearns.
3. 🟢 Ram 14-005-21 — 2021 Ram 1500 with the 5.7L Hemi built 21 August to 2 October 2020: fuel line blockage; replace the engine fuel/EVAP forward line bundle, part 57008587AA.
4. 🟢 GM PIP5187 — 2010-2011 Equinox, Terrain, SRX, CTS, LaCrosse after a cylinder head replacement: put the original fuel rail back.

The fifth, 🟢 Ford's SSM 48573 for 2018-2020 F-150 5.0L, names P0174 with the rich codes P0172, P0173 and P0175, and blames "incorrect flex fuel learning, which is often caused by customer refueling habits or a stuck open evaporative emissions purge valve."

What the list says. Two of the four are software, one is a part on the fuel side, and one is a repair gone wrong. None is an air-fuel sensor, and none is a vacuum leak. When P0174 is alone, the documents point first at calibration and fuel delivery to that bank — and the general physical suspects, an intake gasket or exhaust leak on that side, remain for engines without a document.

What 38 manufacturer documents say about P0174

NHTSA's file holds 84 manufacturer communication records that name P0174. Many are the same document filed again: a revision, a supersession, a re-release under a new number, and one Acura dealer message filed sixteen times between September 2021 and June 2022. Grouped by document, they come to 38, and each one names a cause.

Three things stand out. Software is the largest single lane, at 15 of 38, and seven of those fifteen are Stellantis flash bulletins that list P0174 among many codes. The sensor lane is two documents: one exists to stop an air-fuel sensor being replaced without proof, and the other replaces one only when the codes are traced to it. And no document tells a technician to replace a sensor because P0174 is stored: the ones that replace sensors require the sensor's own codes, or a finding that the sensor caused the lean code. The honest reading is that manufacturers see P0174 as a symptom of air, fuel or calibration, and the sensor as the witness. All 38, with records and lanes.

The Acura file: sixteen requests for parts

Between September 2021 and June 2022, American Honda sent the same dealer message sixteen times. 🟢 It searched for "certain 2016-2020 MDXs, RDXs & TLXs" — and, in the last version, RLXs — "with a client complaint of the Malfunction Indicator Light (MIL) on with the DTC P030X (Cylinder Misfire Detected), P0171 & P0174 (Rear/Front Bank Fuel System Too Lean), or P219A&B (Air-Fuel Ratio Variation of Cylinder) stored," and asked dealers to "collect specific parts from the vehicle prior to you attempting a repair of any kind."

Read in full, the message is narrower than its first line. 🟢 Honda wanted parts only from non-hybrid cars with a misfire code, P0300 to P0306, stored; P0171 and P0174 "may also be stored" but were not required; cars with P0087 or P0088, the fuel pressure codes, did not qualify; and the "Issue has been traced to the fuel injectors," with the original injectors and high-pressure fuel pump still fitted and no repair yet attempted. In other words, this is a fuel injector study — the high-pressure pump in the qualifiers means direct injection — and the lean codes are passengers.

A parts-collection message means the manufacturer is investigating and does not yet have a published fix. The file does not show what Honda found, and we did not find a later bulletin naming a remedy. For an owner of one of these Acuras with lean codes and a misfire, it is a reason to ask for an injector test before an air-fuel sensor, and to ask the dealer, in writing, whether any follow-up bulletin, campaign or goodwill applies before paying for injectors.

Flex fuel and ethanol: when the fuel fools the computer

A flex-fuel engine can run on gasoline, E85 or anything in between. The computer does not measure the ethanol directly on many of them; it infers the blend from how the mixture behaves after a fill-up. If it guesses wrong, it can drive the fuel trims to their limit and set lean or rich codes on a perfectly healthy engine.

The documents. 🟢 Ford's SSM 49050 for 2018-2020 F-150 5.0L trucks blames lean and rich codes on "incorrect flex fuel learning, which is often caused by customer refueling habits when adding only small amounts of fuel, the vehicle mislearning of inferred ethanol fuel mixture (FF_INF value) or a component concern," and the earlier SSM 48573 adds "a stuck open evaporative emissions purge valve." 🟢 Toyota's T-SB-0166-19, which supersedes T-SB-0058-13 for 2009-2018 Sequoia and 2009-2019 Tundra with the 3UR-FBE flex-fuel V8, describes a hard start or light with lean or rich codes where the data show "negative fuel trims and an elevated alcohol density estimate relative to the vehicle's actual fuel alcohol content," and reprograms the engine computer and replaces the fuel pump. It states that "This repair is covered under the Toyota Federal Emission Warranty," in effect "for 96 months or 80,000 miles, whichever occurs first." On a 2019 Tundra, that can still be open in 2026. 🟢 GM's PIP5227 runs the other way: on 2015 trucks and SUVs without the flex-fuel option, if the fuel tests over 10 percent alcohol, flush the fuel system and refill with E10.

The practical rule. If you own a flex-fuel truck with lean or rich codes, tell the shop what you have been putting in the tank and how — small top-ups, switching between E85 and gasoline — before anything is replaced. On a truck without the flex-fuel option, do not put E85 in it.

The PCV file: GM's lean codes that are a hose

All seven air-leak documents are GM's, and four of them are about the positive crankcase ventilation system — the plumbing that draws blow-by gases out of the engine and burns them. It connects the crankcase to the intake, so any break in it is a leak the airflow sensor never sees.

🟢 PIP5341 — 2007-2016 full-size V8s: a PCV tube leaking on the left side. 🟢 PIP5686A — 2019-2020 Silverado and Sierra 1500 5.3L: a foul air tube misinstalled or damaged. 🟢 N192273400 — 2020 light-duty Silverado and Sierra: the right-hand tube not fully seated, with a whistle. 🟢 15317 — 2011 CTS-V: a hose that cracks, replaced under special coverage. And 🟢 21-NA-105 puts "PCV hoses and oil separator connections loose or not completely snapped on" at the top of its inspection before the reprogram.

What these share is that the part is cheap, the diagnosis is a look and a listen, and the parts that usually get replaced instead — an air-fuel sensor, an airflow sensor — cost many times more. On a GM V8 with lean codes and a whistle at idle, the PCV tubes are the first place to look. Our P0171 guide covers the GM camshaft covers with built-in PCV valves, which are the more expensive version of the same story.

What 25 complaints naming P0174 show

The file is small, and that is a finding. Plenty of drivers see P0174 on a scanner, but it is rarely what drives an owner to file a federal safety complaint. When it appears, it is usually one code in a list — with P0171, with misfire codes, with EVAP codes, with a stability-control warning — and the complaint is about the stall or the car's behaviour, not the lean code. Our Check Engine Code Index found the same imbalance for P0174: many bulletins, few complaints.

The five that do not name P0171. A 2002 F-150 whose code turned up at a state inspection. A 2003 Infiniti G35 with P0170 and a violent shake. A 2016 Jeep Cherokee with P0175 and misfires that would not stay running. A 2019 Subaru Outback with P0177, an airflow code and a stall at 60 mph, whose dealer diagnosed a fuel pump and airflow sensor after an earlier fuel pump recall repair. And a 2017 Highlander with a fuel pressure sensor code. None is a clean one-bank lean case; each has another code pointing somewhere more specific.

What the owners did. One replaced a long list of parts on a 2008 Enclave and still had the codes. One paid $523.80 for PCV and purge repairs on a Silverado that did not end the problem. One had a 2017 Maxima throw P0171, P0174 and P219B after a battery change — a reminder that the computer relearns after power loss, and that a code right after a battery job may be the relearn, not a fault. All 25, with notes.

The Toyota pattern: lean codes after a fill-up

All five Toyota complaints connect the trouble to refuelling or to fuel pressure, and three of them are 2017-2019 Highlanders.

A 2019 Highlander owner writes that the check engine light came on with an AWD warning, and "after about 2 days when filling with gas the engine wouldn't start," with P0171 and P0174. A 2017 Highlander owner describes the same sequence — engine light, AWD warning, and after fuelling, knocking and a hard start — with P117B, a fuel pressure sensor range code, and P0174. A third, on a 2019, reports hesitation, sputtering and stalls with P0191, a rail pressure sensor code, P0171 and P0174. The 2020 Avalon owner's hard starts also began after a fill-up.

What the documents say, and what they do not. 🟢 Toyota's T-SB-0009-23 ties lean codes and hard starts to a pump that cannot hold pressure, confirmed on a gauge, and 🟢 the in-tank pump recalls 20V-012 and 20V-682 cover many 2013-2020 Toyota and Lexus models. We did not find a Toyota document naming refuelling as the trigger for these Highlanders, and four complaints are not a pattern Toyota has acknowledged. What they justify is a specific request: a fuel pressure test with a gauge, a VIN check against both recalls and the bulletin, and a note on the repair order that the symptom follows refuelling — which also points a technician at the EVAP purge system.

Can you drive with P0174?

Usually for a short time, if the engine runs normally. The documents and the complaints separate the cases.

P0174 with P0171, engine runs normally. Drive gently, check the oil cap and intake duct, and have it tested within days. A lean mixture raises combustion temperatures and can damage the catalytic converter over weeks.

P0174 with misfires, hesitation or a flashing check engine light. Limit driving. A lean misfire sends unburned fuel into a hot converter.

P0174 with a hard start, stall or loss of power. Treat it as a fuel supply problem until a gauge says otherwise; keep off the highway.

P0174 after a battery change or repair. Drive normally for a few days and see whether it returns, but do not ignore it if it does.

Can you drive with a P0174 code, and for how long? Usually for a few days if the engine idles and accelerates normally, but not for weeks. A lean mixture burns hotter, can misfire under load, and can overheat the catalytic converter, which is the expensive part to lose. In PulsCar's reading of the federal complaint file, 9 of the 25 complaints naming P0174 describe a stall or an engine that would not stay running, and four of those involved fuel pressure or a fuel pump, including a 2008 Tacoma that stalled climbing a bridge at 60 mph. If the code comes with a flashing light, misfires, hesitation or a hard start, limit driving and have the fuel pressure and fuel trims checked first. If it comes alone on an engine that runs well, check the oil cap, intake duct and PCV hoses today.

Should you buy a used car with a P0174 history?

Usually yes, if the history is documented and the cause was found. Ask for the repair order: a PCV tube, an intake duct or a reprogram under a named bulletin is a closed case. A car whose lean codes were cleared without a repair, or that had an air-fuel sensor replaced with no sensor code on the paperwork, is an open one. On a 2017-2021 Nissan Armada, Titan or NV or a 2016-2019 QX80, ask whether NTB20-009A or ITB20-005 was performed. On a 2020-2021 Colorado or Canyon 3.6L, ask for 21-NA-105. On a Toyota or Lexus, confirm the fuel pump recalls. On the test drive, connect a scanner and read the long-term fuel trims on both banks with the engine warm; numbers that are high and similar on both banks mean the cause is still there.

Clearing P0174 before an inspection

A car with P0174 stored will usually fail an emissions inspection, and clearing the code does not help: the readiness monitors reset with it and the station sees an incomplete system, and a real lean condition will set the code again. What works is to fix the cause, then drive a mix of city and highway until the monitors report ready. After a reprogram, the relearn procedures in the bulletin matter — Infiniti's ITB20-005 lists throttle and idle air volume learning after the update — and a car that has not completed them may not idle or trim correctly on the way to the station.

What a shop actually does with a P0174, checkpoint by checkpoint

1. Reads every code and the freeze-frame data, noting P0171, airflow, fuel pressure, misfire and EVAP codes.
2. Checks bulletins and campaigns on the VIN, including engine computer part-number checks on Nissan and Infiniti.
3. Compares fuel trims on both banks at idle and at 2,500 rpm.
4. Inspects the oil cap, dipstick, intake duct and PCV tubes, and listens for a hiss.
5. Smoke-tests the intake, PCV and EVAP systems.
6. Measures fuel pressure with a gauge, at idle and under load.
7. Checks the airflow sensor reading against expected values, and inspects the air box.
8. Replaces a sensor only on evidence — its own code, or a test showing it misreading.

Three P0174 traps that cost owners the most

Trap 1: the sensor that reported the problem. The bank 2 air-fuel sensor is usually telling the truth about a lean mixture. Lesson: no sensor without a sensor code or a test — Nissan's bulletin says it in capitals.

Trap 2: treating two codes as two faults. P0171 and P0174 together usually have one shared cause. Lesson: fix what the banks share before anything on one side.

Trap 3: the free fix nobody checked. Several of the clearest answers are reprograms that apply only to listed part numbers or build dates. Lesson: ask for a bulletin and part-number check before paying for parts.

Three P0174 quotes, decoded

These are composite scenarios, not individual customers: each combines details that come up repeatedly in owner reports and shop quotes.

Scenario 1: 2015 Silverado 1500 5.3L, 118,000 miles, P0171 and P0174, whistle at idle, quote $480 for two oxygen sensors. The owner asks for a smoke test first. A PCV tube on one side is cracked; it is replaced for under $100 with labor, the trims return to normal and the codes do not come back. Lesson: both banks lean, look at what they share.

Scenario 2: 2019 Nissan Titan 5.6L, 52,000 miles, P0174 only, quote $390 for a bank 2 air-fuel sensor. The owner asks the dealer to check NTB20-009A. The engine computer part number is in the table; it is reprogrammed, and the code does not return. Lesson: P0174 alone on a VK56 is a part-number question first.

Scenario 3: 2017 Highlander, 104,000 miles, lean codes and a hard start after fuelling, quote $1,300 for a fuel pump. The owner asks for a gauge reading and a recall check. The pressure is low on a cold start; the VIN is not on the recall, and the owner asks Toyota customer relations for goodwill with the bulletin number and the gauge reading attached before paying. Lesson: measure, then check the VIN, then pay.

The P0174 plan: 10 minutes, today, this week

In the next 10 minutes: read all the codes, check the oil cap and dipstick, squeeze the intake duct, listen for a hiss, and note when the light came on.

Today: if P0174 is alone, search for a bulletin by VIN; if P0171 is with it, look at the PCV tubes and intake before anything else. Run the VIN for fuel pump recalls on a Toyota or Lexus.

This week: have the fuel trims compared at two engine speeds, a smoke test done, and, if the trims point at fuel, a pressure test. Replace a sensor only when its own code or a test names it.

If you are not sure whether a whistle or hiss you hear under the hood is related, PulsCar's free sound check screens a 30-second recording of your engine. It does not read codes; it is a second opinion on what the engine sounds like.

Sources and documents

Primary documents only. Where a claim in this guide is marked 🟢, it rests on one of the items below, and the reference is given so you can pull the document yourself. Claims marked ⚪ are shop-price estimates carried from PulsCar's repair guides — estimates, not measurements from a dataset we own.

1. Nissan NTB20-009A (June 2021; 2017-2019 Armada, 2017-2021 NV, 2017-2019 Titan and Titan XD, VK56VD; only P0174) and Infiniti ITB20-005 (February 2020; 2016-2019 QX80). NHTSA documents 10199168, 10172179.
2. Nissan NTB19-022 and Infiniti ITB19-007 (March 2019; do not replace the A/F sensor without P2096-P2099), NTB19-030 and ITB19-010 (VQ35; engine computer reprogram), ITB11054A and ITB15004. NHTSA documents 10158432, 10158424, 10160183, 10160178, 10192103, 10192515.
3. GM 21-NA-105 (May 2021; 2020-2021 Colorado and Canyon 3.6L; ECM reprogramming covered 8 years/80,000 miles) and 22-NA-171 (January 2023; intake boot). NHTSA documents 10194116, 10231421.
4. GM PIP5341, PIP5686, service update N192273400 and special coverage 15317 (PCV); PIP5446 and PIP4813B (air box and airflow sensor); PIP5227 (ethanol); PIP5187 (fuel rail after head replacement); PI1438, PIE0433 and PIE0413.
5. Ford SSM 48573 and SSM 49050 (flex-fuel learning), TSB 21-2443, 21-2083, 21-2154, 22-2393 (5.0L software), 18-2270, 18-2310, 20-2324 (2.7L), 17-0014, 18-2321, 19-2091 and 21-2106 (Transit).
6. Toyota T-SB-0166-19 Rev1 (supersedes T-SB-0058-13; Tundra and Sequoia 3UR-FBE; Federal Emission Warranty, 96 months or 80,000 miles), T-SB-0009-23 and Lexus LSB000523 (fuel pump). NHTSA recalls 20V-012 and 20V-682 (Toyota and Lexus in-tank fuel pump). NHTSA documents 10171454, 10235216, 10235215.
7. Stellantis 14-005-21 (July 2021; 2021 Ram 1500 5.7L built 21 August to 2 October 2020; fuel line bundle), 09-025-25 (August 2025; 3.0L Hurricane HO built 16 September 2024 to 7 June 2025; purge line), and flash bulletins 18-057-16, 18-002-19, 1806917, 18-050-21, 1814522, 21-029-16, 1810723.
8. American Honda dealer message, September 2021 to June 2022, sixteen versions: parts collection for 2016-2020 Acura MDX, RDX, TLX and RLX with a misfire code stored, lean codes optional, issue traced to the fuel injectors. NHTSA document 10213569.
9. Land Rover SWA09013 (2002-2005 Freelander fuel filter).
10. PulsCar Check Engine Code Index: 48 bulletins naming P0174 by the index method, software in at least 19.
11. PulsCar analysis of NHTSA public data, September 2026: 25 complaints naming P0174, read in full; 84 manufacturer records grouped into 38 documents. Data and method.

For the neighboring codes: P0171 bank 1 lean, P0101 airflow, P0087 fuel pressure, P0300 misfires and the code index. For the symptoms: car running rough, car shaking when idle, car stalls while driving, car hesitation when accelerating and fuel pump replacement cost. For the trucks: F-150, Silverado and Tundra.

Methodology. Complaint counts come from NHTSA's public complaint file with case-insensitive matching on the code; all 25 complaints were read in full. The 84 manufacturer records naming P0174 were grouped into 38 documents by bulletin number and text, and each was assigned one lane by reading it; 15 of the 38 were downloaded and read in full from the primary document — two of those reads changed our first classification — and the rest in NHTSA's published summary text. Recall searches cover NHTSA's recall file from 2010. Price ranges marked ⚪ are US estimates carried from our repair guides. Nothing here is a failure rate.

Prices verified July to September 2026 in the repair guides they are carried from, and reviewed quarterly — nothing on this page was re-priced this pass, because the estimator pages we would use refused automated checks in September 2026. Technical documents verified September 2026: Nissan NTB20-009A, NTB19-022 and NTB19-030, Infiniti ITB20-005 and ITB19-010, GM 21-NA-105, 22-NA-171, PIP5686A and N192273400, Toyota T-SB-0166-19 and T-SB-0009-23, Ford SSM 48573, SSM 49050 and TSB 20-2324, Stellantis 14-005-21 and 09-025-25, and the American Honda dealer message of May 2022 were downloaded from static.nhtsa.gov and read in full on 24 September 2026; the remaining bulletins were read in NHTSA's published summary text the same day, when the complaint, recall and bulletin files behind our analysis were also queried.

Had a P0174 fixed by a reprogram, a hose or a pump — or by none of them? Email [email protected] with the vehicle, mileage and what finally worked.