P0420 Code in 2026: $0 to $4,500, and Five Checks Before You Buy a Catalytic Converter

P0420 is a verdict on two sensor readings, not a death certificate for your catalytic converter. The computer watches oxygen before and after the catalyst; when the "after" signal starts to look too much like the "before" signal, it decides the catalyst is not doing its job.

Plenty of things make that comparison look bad while the converter is fine. Subaru's P0420 procedure, bulletin 09-110-23R, checks other codes, oil smoke, exhaust leaks and the air-fuel sensor before it approves replacing the exhaust pipes that carry the catalyst. GM wrote the same thing more bluntly on its heavy-duty trucks: an exhaust leak repair "must be attempted before considering the replacement of a catalytic convertor."

By the end of this guide you will know which of five routes your P0420 belongs to, what proves it, and what each one costs — from a $0 VIN check to a $4,500 dealer converter. Claims marked 🟢 rest on a document in Sources, opened and read; ⚪ marks estimates and owner reports.

I built Pulscar — an AI tool that identifies car problems from a 30-second recording — after spending $6,000 on misdiagnosed repairs, starting with a $380 bill for a rattle three people had called "probably your catalytic converter," which turned out to be a $5 heat shield.

How to use this guide

Every route is defined by what you can hear and what the data shows, not by the code.

One rule overrides everything: fix what feeds the converter before you replace the converter. A misfire or an oil-burning engine will fail a new converter the same way it failed the old one, and the second one is rarely covered.

First: is this really P0420, and which side?

Write down every code stored with it; three splits remove most of the confusion.

P0420 or P0430? A bank is a row of cylinders. A four-cylinder engine has one row, so it can only set P0420. A V6 or V8 has two rows, usually one catalyst per row: P0420 is bank 1, P0430 is bank 2. Bank 1 is the side with cylinder number 1, and it is not always the side you guess. Honda's documents for the Pilot, Ridgeline and Odyssey V6 call P0420 the "rear bank" and P0430 the "front bank."

P0420 alone, or with friends? A misfire code (P0300 to P0306), a lean or rich code (P0171, P0172), an oxygen or air-fuel sensor code, or a fuel system code stored alongside P0420 almost always outranks it. Subaru fixes those first and re-tests.

What does it sound like? A rattle under the middle of the car suggests broken catalyst or a loose heat shield; a tick or puff on a cold start that fades points at an exhaust leak. Toyota's T-SB-0161-13 ties a catalyst rattle to P0420 in one line.

The 10-minute driveway protocol

1. Read the codes and save them before anyone clears them. A $20 to $40 Bluetooth reader gives you every stored code and the freeze frame. Clearing first throws that evidence away.
2. Look at the dashboard while the engine idles. Flashing light or a shaking engine means a live misfire: Route 2, and the rest of this protocol can wait.
3. Start the car cold and listen at the back, then crouch by the front wheel. A tick or puff that fades within a minute or two is a leak candidate: Route 1. Record 30 seconds.
4. With the engine off and cool, tap the converter shell with your palm or a rubber mallet. A loose rattle from inside the shell is substrate; a tinny buzz from the outer skin is a heat shield.
5. Look at the tailpipe on a revving start. Lingering blue or white smoke means oil or coolant is reaching the catalyst.
6. Run the VIN through NHTSA's recall lookup and your manufacturer's owner site. On several cars this step ends the story at $0: Route 4.
7. Write down the odometer and the vehicle's in-service date. Under 8 years and 80,000 miles, the federal emissions warranty applies to the converter itself: Route 5.

Ten minutes, a cheap reader and a phone, and you have done most of what a $80 to $200 diagnostic fee buys. What a diagnostic should cost covers the rest.

Find your situation: eight ways people arrive here

"The light came on right after exhaust or muffler work." → Route 1. A disturbed joint ahead of the rear sensor is the first suspect.

"Light is flashing and the car shakes." → Route 2, today. The misfire is the emergency; P0420 is the consequence.

"Shop says new converter, $2,000, just from the code." → Route 3. Ask what the sensor data showed, and whether they checked for software.

"2012-2016 Kia Soul with P0420." → Route 4. Recall 19V-120, and for cars that already had it done, SC176Y.

"Honda Pilot, Ridgeline or Odyssey V6 with P0420 or P0430." → Route 4, then Route 2: Honda's extensions cover fuel injectors on these engines.

"Rattle underneath and the car feels slower uphill." → Route 5. Broken or clogged substrate; the uphill power guide covers other causes.

"I cleared it to pass inspection and it came back." → The inspection section below: it returns whenever the cause is real.

"Smells of rotten eggs or fuel." → Route 2 or 5. Sulfur means an overloaded catalyst, raw fuel means unburned fuel; the gas smell guide sorts the rest.

What actually determines your number

Whether the converter is the cause or the victim. A leak, sensor or software is a two- or three-figure repair; a converter killed by an unfixed misfire becomes two converters.

What is stored next to P0420. Kia's SC176Y flowchart shows why: P0420 alone gets a converter, P0420 with an active misfire code gets a compression test, and a failed cylinder gets an engine.

Your VIN. Campaigns are defined by build dates and engines, not symptoms: inside, free; one day outside, yours.

Age and mileage against the emissions warranty. Under 8 years and 80,000 miles, the converter is a federally warranted part. California's 13 CCR 2037 adds 7 years or 70,000 miles for high-priced parts.

Where the converter lives. A bolt-in underfloor converter is 1 to 2 hours of labour; one built into the exhaust manifold, as on the 2019 Tucson 2.0, costs more.

Aftermarket rules in your state. Where CARB rules apply, a replacement must carry an approval number and the cheapest universal converter is off the table.

The price ladder: read it from the bottom up

Read it from the bottom up: the last line and the top line are the same converter, separated by a VIN, an odometer and a diagnosis.

Your number, by what you drive

Two rows break the pattern. On the F-150 hybrid Ford says the warning itself may be wrong. On the Traverse and Enclave the coverage never names P0420; it describes a hole and a rattle in the front pipe, the kind of leak Route 1 is about.

Which route is yours? Five questions

1. Did the code appear after exhaust work, or is there a tick or puff on a cold start? → Route 1. A leak ahead of the rear sensor.

2. Is the light flashing, or is a misfire, lean, rich or fuel code stored with P0420? → Route 2. Fix the engine before the exhaust.

3. Lone P0420, smooth engine, no rattle, no smell? → Route 3. Sensors, air intake and software, proven with data.

4. Does your VIN appear on a recall, emission recall or extension? → Route 4. Run this one first whatever else you answered.

5. Is there a rattle inside the converter shell, lost power at speed, or a sulfur smell, with everything above ruled out? → Route 5. The converter itself, and the warranty clock.

The five routes, cheapest first

Route 1 · The code came with a leak — exhaust leaks ahead of the rear sensor

The tell. A tick or puff under the car on a cold start that quietens as the exhaust warms, and soot streaks at a flange or clamp. Often after a muffler, hitch or pipe job.

What it actually is. A leak between the engine and the rear oxygen sensor lets outside air into the exhaust, and the sensor's reading stops meaning what the computer thinks. GM's preliminary information PIP5110C, for 2011-2015 Silverado and Sierra heavy-duty trucks, Express and Savana vans with the 4.8L and 6.0L engines, tells technicians with a lone P0420 to check for "a possible leak in the exhaust system behind the bank 1 sensor 2 O2 sensor" and adds: "This repair must be attempted before considering the replacement of a catalytic convertor."

The cheap cause that gets skipped. Clearance. The same GM document says that if the truck has an aftermarket utility bed or trailer hitch, check for "a minimum of 1.5" to 2" of exhaust system clearance" and fit a new clamp. On 2019 and 2021 Traverse and Enclave models, GM's special coverages replace a front pipe where "a hole may develop in the exhaust pipe at the bracket location."

Fix it yourself — find the leak, do not chase it with sealant. Cold engine, parking brake on. Have someone start it while you listen along the exhaust from the front wheel back to the converter, look for soot tracks at every flange, and hold a hand a few inches from joints, never on them, to feel for a pulse. Record 30 seconds at each suspect joint. The honest limit: use stands, not a jack alone, and a cracked flex section or manifold is welding work, not a DIY wrap.

Where this does not apply. A tick from the top of the engine that does not fade when hot is valvetrain or injectors; the ticking guide sorts those.

At the shop — say this: "P0420 with a cold-start tick underneath. Before any converter quote, pressure- or smoke-test the exhaust from the manifold to the rear oxygen sensor and show me any leak you find."

Route 2 · Something is feeding the converter — misfire, fuel or oil first

The tell. A flashing light, rough idle, stumble, raw fuel smell or smoke. On the reader: P0300 to P0306, P0171, P0172, or on a Honda V6 P219A and P219B, beside P0420.

What it actually is. A cylinder that does not fire pushes unburned fuel into the exhaust, and the catalyst burns it, which is how converters overheat. Oil and coolant do the slower version, coating the catalyst. Honda's bulletin 20-100 for the 2016 Pilot names both: "The PCM software may misinterpret sensor inputs as a deteriorated catalytic converter," and injector debris "can cause internal wear or clogging inside one or more injectors." Its fix for P0420 or P0430 alone is software plus a cylinder air-fuel test, with injectors replaced only if that test fails. Letter 21-010 extends injector cover on later Pilot, Ridgeline and Odyssey years to 10 years or 150,000 miles.

The cheap cause that gets skipped. The history codes and the freeze frame. On the 2015-2016 Fit, Honda's bulletin 18-027 says outright that faulty injectors "may be affecting combustion and causing a false DTC P0420." A shop that quotes a converter without reading those codes has not diagnosed the car.

Fix it yourself — prove where the misfire lives. On an engine with individual coils, note which cylinder the misfire code names, swap that coil with its neighbour, clear the misfire counter and drive. If the misfire moves with the coil, the coil is the part. The honest limit: direct-injection injectors, compression tests and oil-burning diagnosis are shop work. The flashing light guide walks the rest.

Where this does not apply. A misfire that is gone and a P0420 that stays can mean the misfire already damaged the catalyst: Route 5, but with the cause fixed first.

At the shop — say this: "P0420 with a misfire history. Print every stored and pending code and the freeze frame. Check for any injector extension on this VIN, and do not quote a converter until the misfire is fixed and the catalyst monitor has run again."

How do you tell a broken converter from an exhaust leak without lifting the car? By ear, and more reliably than most people expect, because the two failures make opposite kinds of sound. Broken catalyst substrate is loose material inside a steel shell, so it rattles: a gravelly shake from under the middle of the car, loudest at idle and when the shell is tapped. Toyota's Tacoma bulletin files that exact noise under P0420. An exhaust leak is gas escaping at a joint, so it ticks or puffs in time with the engine, loudest when the metal is cold and tightening as it warms. Record 30 seconds near the rear of the car on a cold start, and Pulscar's AI compares the recording against catalogued failure patterns, then returns the likely cause, whether it is safe to drive, and the fair 2026 price. Free, no card, no subscription, about ten minutes. The report arrives by email. More rattles are in the rattling noise guide.

Route 3 · The car only thinks the converter failed — sensors, intake air and software

The tell. A lone P0420, a smooth engine, normal power, no smell and no rattle. Often it comes and goes, or returns a few weeks after being cleared.

What it actually is. Every piece of the measurement can fail without the catalyst failing. Subaru's active test makes the sensor question binary: the technician commands fuel changes and watches whether the air-fuel sensor follows. If it does not, "Replace the A/F sensor assembly"; only if it does are the exhaust pipes replaced. Software is the other half. GM's 18-NA-331 says P0420 on 2013-2015 Trax and Encore 1.4L cars "may be caused by a software anomaly," a 0.3-hour reprogram with no parts. Ford's 25-2188 calls P0420 on 2022-2024 Explorer 2.3L models built from 3 January 2022 "an incorrectly illuminated MIL" and reprograms it in 0.4 hours. Kia's ENG 160 says P0420 on several 2.4 GDI Optima, Sorento and Sportage models "occurs most commonly during prolonged engine braking while descending a steep grade."

The cheap cause that gets skipped. The air filter lid. GM's 16-NA-111, for V8 trucks, SUVs, Camaro, Corvette, CTS and Escalade models, traces P0420 and P0430 to sand and debris bypassing a badly seated air filter, damaging the oxygen sensor element and blocking the converter, and instructs: "Do not replace any of the parts until the air filter housing has been validated to be completely sealed."

Fix it yourself — get the numbers, then check the cheap parts. Many inexpensive readers show "Mode 6" test results, the computer's own catalyst score against its limit; write down the value and the limit. At a steady 2,500 rpm on a warm engine, a live graph should show the front sensor switching quickly and the rear sensor far calmer; a rear trace that copies the front one is what the computer is complaining about. Then open the air box, check that the filter seats and the clips close, and look for dust on the clean side. The honest limit: a reader cannot run Subaru's commanded fuel test or install a manufacturer calibration; that is dealer or well-equipped independent work.

Where this does not apply. If the rear sensor is copying the front one and the car rattles, or the engine is misfiring, the sensor is reporting a real problem: Routes 2 or 5. The oxygen sensor cost guide covers which sensor is which.

At the shop — say this: "Before any parts, check for software updates or bulletins for P0420 on this VIN. Then show me the Mode 6 catalyst result against its limit and a graph of both oxygen sensors. If a sensor is condemned, tell me which test condemned it."

Route 4 · Your VIN is on a document — recalls, emission recalls and extensions

The tell. Your car is in the table above, or a recall letter arrived unopened.

What it actually is: the Kia Soul story. Recall 19V-120, submitted 22 February 2019, covers 378,967 2012-2016 Soul cars with the 1.6L GDI engine built 8 July 2011 to 11 August 2016, with an estimated 1 percent defect rate. Kia's Part 573 report names the cause as "Inaccurate Catalytic Overheating Protection (COP) ECU logic parameters and overheating of the catalytic converter." If substrate reaches the cylinders, pistons can be damaged and a fire can follow. The warnings it lists are "Illumination of the Malfunction Indicator Lamp (MIL) and/or engine knocking noise." Kia's dealer procedure turns that into a flowchart keyed to P0420: software for every car, a converter if P0420 is stored, a compression test if a misfire code is active, and an engine if any cylinder is under the 149 psi minimum. Kia corrected the logic in production on 27 July 2016 for the 2017 model year.

The follow-up most owners never hear about. In October 2024 Kia issued SC176Y, revised 23 March 2026, for Souls from the same build window "that previously had the recall campaign SC176 completed" and now store P0420 as active, history or pending. Same logic, no charge to the owner, and the dealer can claim a rideshare or up to three days of rental.

The cheap cause that gets skipped. Keeping the evidence. SC176Y states that the repair "can only be initiated/opened with a DTC P0420." Clear it before the dealer visit and you can erase the one thing that opens a free converter. Delay has its own cost: Honda's injector letter warns that putting off an emissions repair "could be determined as lack of proper maintenance of your vehicle."

The other lists. Ford's emission recall 24E04 covers 90,892 F-150 hybrids whose OBD system "may falsely set" P0420 and P0430; dealers reprogram, and replace a converter only if its test value exceeds 0.4. The Honda and GM programmes are in the table above.

Where this does not apply. Every 2017 or later Soul is outside 19V-120, and so is any Soul with the 2.0L engine; the Kia Soul guide covers their separate campaigns. Being the right model year is not eligibility: Kia's report says the recalled cars "were not produced in VIN order," which is why some owners in our sample found their VIN not listed.

At the shop — say this: "Run this VIN for every recall, emission recall, special coverage and warranty extension, open or completed. P0420 is still stored; do not clear it before you check SC176Y or any programme that needs the code."

Which P0420 repairs do manufacturers pay for, and which are yours? The answer is written into documents, not left to a service adviser's mood. A 2012-2016 Soul 1.6 built between 8 July 2011 and 11 August 2016 sits inside recall 19V-120, and if it had that recall done and stores P0420 again, inside SC176Y: converter free, compression test on a misfire, engine if a cylinder fails. A 2022-2023 F-150 hybrid sits inside emission recall 24E04, where Ford says the warning may be false. Honda's V6 Pilot, Ridgeline and Odyssey years carry injector cover to 10 years or 150,000 miles. And every light-duty vehicle has the federal emissions warranty on the converter for 8 years or 80,000 miles. Against that, a leak caused by a hitch, a misfire from worn plugs, and a converter poisoned by an engine burning oil are yours. Pulscar tells you which sound family you have before the conversation about who pays begins.

Route 5 · The converter really has failed — rattle, lost power, and the warranty clock

The tell. A loose rattle inside the converter shell when the engine idles or the shell is tapped. Power that fades at speed or uphill, heat through the floor, a strong rotten egg smell. And a catalyst test value that stays failed after Routes 1 to 4 are ruled out.

What it actually is. The honeycomb inside has melted, cracked or been coated. Toyota's bulletin T-SB-0161-13, for 2010 Tacoma models with the 2TR-FE engine, describes a "front exhaust pipe catalyst rattle noise and/or MIL 'ON' condition with DTC P0420" and replaces the front exhaust pipe assembly in 0.7 hours. On the 2019 Tucson 2.0L GDI, Hyundai's 20-FL-010H pairs an ECM update with "replacement of the exhaust manifold catalyst." A clogged converter is urgent in a way an inefficient one is not; the converter cost guide explains the difference.

The cheap cause that gets skipped. The warranty clock. Federal law requires that for light-duty vehicles from model year 1995, the warranty on a "specified major emission control component" runs 8 years or 80,000 miles, and it defines that term as "only a catalytic converter, an electronic emissions control unit, and an onboard emissions diagnostic device." Toyota's Tacoma bulletin applies exactly that: "96 months or 80,000 miles, whichever occurs first, from the vehicle's in-service date." In California, 13 CCR 2037 requires 7 years or 70,000 miles on high-priced warranted parts. The clock starts at the in-service date, not the model year, so a late-sold car may still be inside it.

Where this does not apply. A tinny buzz from the outside of the shell is a heat shield, not substrate. And a converter destroyed by a misfire or burning oil will fail again unless Route 2 comes first; manufacturers can decline warranty cover for damage from an unrepaired cause.

At the shop — say this: "Give me the in-service date and mileage against the 8-year, 80,000-mile emissions warranty before you quote. If it is outside, quote direct-fit and OEM side by side, and write down what caused the failure."

What does it actually cost to fix P0420 in 2026? It is two very different price lists with one diagnosis between them. On the short list: a code read at $0 to $40, a diagnostic fee of $80 to $150 at an independent or $120 to $200 at a dealer, an exhaust leak repair at $100 to $400, a downstream oxygen sensor at $200 to $400 installed, a misfire repair at $150 to $400, and software that GM's and Ford's bulletins allow 0.3 to 0.4 hours for. On the long list: a universal converter at $200 to $600 where it is legal, a direct-fit aftermarket unit at $700 to $1,600, an OEM converter at $1,500 to $2,500 independent and up to $4,500 at a dealer. The same converter costs $0 inside 19V-120, SC176Y, 24E04 or the 8-year federal warranty. Pulscar prices your recording against those rungs before anyone quotes you theirs.

Rattle or tick: telling the two sounds apart

Your ears save money here, because the cheap and expensive causes of P0420 sound nothing alike.

The catalyst rattle. Dry and granular, like gravel in a tin, from under the middle of the car, loudest at idle and when you tap the cold shell. In our complaint sample a 2014 Soul owner listed a "rattling sound from the exhaust" alongside a cylinder with no compression.

The heat shield buzz. Tinny, from the outer skin, often at one engine speed only. A $5 clamp fixes it, and it can sit on top of a real converter rattle, so tap both the shell and the shield.

The exhaust leak tick. Sharp and in time with the engine, or a soft puff, loudest cold and fading within a couple of minutes as the joint expands.

The valvetrain tick. Same rhythm from the top of the engine, not fading with heat; our study of noises without a warning light shows how often owners hear trouble first.

Record from the same spot each time, engine cold, phone a foot from the source.

What we counted in the federal complaint file

Our sample: every vehicle complaint added to NHTSA's public complaint files between 1 January 2015 and 8 September 2026, pulled 14 September 2026 and de-duplicated by report number: 777,040 unique owner reports. We matched the exact code in the owner's description.

The converter dominates the story owners tell. 302 complaints contain the exact string "P0420"; allowing the common typo "P420" raises that to 313. 232 of the 302 mention the catalytic converter. Only 36 mention a misfire or a P030X code, 35 an oxygen or air-fuel sensor, and just 5 the words "exhaust leak." Manufacturers check those first; owners mostly report hearing about the converter.

One car dominates the count. The Kia Soul accounts for 84 of the 302, 73 of them on 2012-2016 models, and 30 of those Soul complaints cite recall 19V-120 or campaign SC176 by number. Several describe a recall letter and a VIN the lookup did not list. After the Soul come the Ford Focus with 15, the Hyundai Tucson with 12, the Honda Pilot with 10, and the Chevrolet Equinox and Traverse with 9 each. These are raw counts from very different sales volumes, so they are not a reliability ranking.

Bank 2 has its own story. 106 complaints name P0430, and 42 of them are Honda Pilots, mostly 2016, 2017 and 2019 models. Across the 46 Pilot complaints naming either code, 33 mention the fuel injectors, the part Honda's extensions cover. 24 complaints name both P0420 and P0430.

Where owners stated a mileage (98 of the 302), the median was 108,829 miles, well past the federal 80,000-mile converter warranty. Complaints are owner reports: a converter mentioned in a complaint was not necessarily the part at fault.

Clearing P0420 before an inspection: why it comes back

Clearing the code the morning of the test fails for three documented reasons.

The light is an automatic fail. Under 40 CFR 85.2222, the federal procedure for OBD inspections, a vehicle whose check engine light is commanded on "shall fail the OBD inspection."

A freshly cleared car is not ready. The same rule allows 2001 and newer vehicles no more than one unset readiness monitor. Clearing codes resets the monitors, and the catalyst monitor needs specific driving to run again: Subaru's procedure idles the car five minutes, holds 37 mph until the catalyst reaches 500 degrees Celsius, then lifts off for a fuel cut.

When the monitor runs, the code returns. If the cause is real, the car sets P0420 again as soon as the test completes. Honda's owner letter for 2017-2019 Pilots says it without hedging: "If your vehicle's MIL is on, it may fail a state or local emissions inspection."

The honest route to a pass is the repair, the drive cycle, and a readiness check with your own reader before you queue.

What actually happens at the shop, checkpoint by checkpoint

Checkpoint 1 — the VIN question. "What recalls, emission recalls, special coverages and extensions show on this VIN, open or completed?" Free, and on Route 4 cars it decides everything.

Checkpoint 2 — the full code list. "Which codes are stored, pending and in history, and what does the freeze frame say?" A misfire in history changes the job.

Checkpoint 3 — the leak check. "Was the exhaust checked for leaks between the engine and the rear oxygen sensor, and how?" GM puts this before any converter.

Checkpoint 4 — the data and the software. "What is the Mode 6 catalyst result against its limit, did the air-fuel sensor pass an active test, and is there a calibration update for P0420 on this engine?" Subaru decides between a sensor and a pipe on that result.

Checkpoint 5 — the fee, the warranty and the ceiling. "What is the diagnostic charge, is the converter inside the 8-year, 80,000-mile emissions warranty, and will you call me before anything over this figure?" The overcharging guide covers how quotes inflate.

Three diagnostic traps that cost owners the most

Trap 1: the converter quoted from the code. The situation: a lone P0420, a smooth engine, 110,000 miles. What the shop says: "P0420 is the catalytic converter. Direct-fit is sixteen hundred, OEM is more." What is really happening: nobody has checked for a leak, graphed a sensor or looked for software. Subaru's procedure puts four steps ahead of the exhaust pipes; GM's says the leak repair "must be attempted" first. Price versus bill: $100 to $400 for a leak or sensor, or $0 for software in warranty, against $700 to $4,500. Your protective question: "What did the leak check, the sensor data and the bulletin search show before you chose the converter?"

Trap 2: the code cleared before the free repair. The situation: a 2014 Soul 1.6 that had SC176 in 2019, P0420 back, and a quick-lube offering to "reset the light." What the shop says: "It's probably nothing. We'll clear it and see if it comes back." What is really happening: SC176Y "can only be initiated/opened with a DTC P0420," active, history or pending. Clearing it can close the door on a free converter until the fault resets. Price versus bill: $0 for the campaign converter, against owner-reported converter quotes in the thousands. Your protective question: "Can you read and save the codes without clearing them, so the dealer can check SC176Y?"

Trap 3: the new converter on a misfiring engine. The situation: P0420 with a history misfire on cylinder 3 and a 2017 Pilot at 96,000 miles. What the shop says: "Your cat is bad. Once it's replaced the misfire will settle down." What is really happening: the order is backwards. Honda fixes software and injectors first, under a 10-year, 150,000-mile injector extension. Price versus bill: $0 for injectors under the extension, against a converter and then, when the misfire returns, another converter. Your protective question: "Does this VIN have the injector extension, and has the misfire been repaired before any converter?"

Three quotes, decoded

These are composite scenarios, not individual customers — the mileages and outcomes are typical of the pattern each describes, assembled so the arithmetic is visible. We do not publish invented testimonials.

Scenario 1 — the rattle that was a pipe. A 2019 Traverse at 72,000 miles with P0420 and a rattle underneath. The first quote is a front converter at $1,800. The owner runs the VIN, finds special coverage N212356540, and the dealer replaces the front exhaust pipe with its separated bracket at no charge. The coverage names a hole and a rattle, not P0420, so the code is re-checked after the pipe before anything else is bought. Lesson: a rattle with P0420 is two facts, and the cheaper one can be free.

Scenario 2 — the V6 that needed injectors. A 2016 Pilot at 104,000 miles with P0430 and a history misfire. A converter is quoted on the code. Honda's 20-100 applies: the dealer updates the software, runs the cylinder air-fuel test, replaces the injectors under the 10-year extension, and the converters stay. Lesson: on a documented engine, the manufacturer's order of work is also the cheapest order.

Scenario 3 — the Subaru that failed the test honestly. A 2018 Crosstrek at 76,000 miles, now past eight years in service, lone P0420. An independent shop follows 09-110-23R: no other codes, no smoke, no leak. The air-fuel sensor fails the active test and is replaced for about $300. The catalyst value then clears the bulletin's limit, and the $1,400 to $2,800 pipe quote never happens. Lesson: a test with a number and a limit is worth more than any opinion about the converter.

Your situation right now: four playbooks

"The light is flashing." Slow down, avoid highways, hills and towing, and get to a shop today. The converter is at risk until the misfire stops.

"Steady P0420, car drives fine." Read and save the codes, run the VIN, listen on a cold start, tap the shell. Book a diagnosis this week, not a converter.

"A shop has quoted a converter." Ask for the leak check, the sensor data or Mode 6 result, the bulletin search and the in-service date, in writing. If they cannot provide them, get a second opinion; the dispute guide covers a bill that already went ahead.

"My car is on one of the lists." Do not clear the code. Call the dealer with the campaign number and keep the letter. If you already paid, both Kia's recall letter and GM's special coverages describe reimbursement.

After the fix: verify, then prevent

Verify the monitor, not just the light. A light that stays off for a day proves nothing. Drive for a week, then check with your reader that the catalyst monitor shows complete and P0420 has not returned as pending.

Fix the cause and keep the paperwork. The invoice should name what killed the old converter and how that was repaired.

Protect the new converter. Treat a flashing light as a stop-soon event, fix oil burning before it becomes a second converter, and keep the air filter box sealed. The check engine light guide covers the next light.

Record a healthy baseline. Thirty seconds of a cold start from under the rear of the car, saved now, turns the next rattle into a comparison instead of an argument. The recording guide has the method.

Your action plan: 10 minutes, today, this week

Next 10 minutes — free:

1. Read and save every code and the freeze frame. Do not clear anything.
2. Check whether the light is flashing, and whether the engine is smooth.
3. Listen on a cold start for a rattle or a tick, and record 30 seconds.

Today:

4. Run the VIN through NHTSA's recall lookup and the manufacturer's owner site.
5. Note the in-service date and mileage against 8 years and 80,000 miles.
6. Run a free sound check before anyone quotes a converter.

This week:

7. Get a written leak check, sensor data or Mode 6 result, and a bulletin search.
8. Fix leaks, misfires, sensors or software first, then drive until the catalyst monitor completes.
9. Only then, and only if the test still fails, price a converter against the warranty.

Sources and documents

Primary documents only. Where a claim is marked 🟢 it rests on an item below, opened and read, with every population, date and quoted phrase taken from the document itself. Claims marked ⚪ are estimates or owner reports.

1. NHTSA 19V-120 / Kia SC176 — Part 573, 22 February 2019: 378,967 2012-2016 Soul 1.6L GDI built 8 July 2011 to 11 August 2016; 1 percent estimated; logic corrected 27 July 2016. Part 573 (PDF) · Owner letter (PDF) · Dealer procedure (PDF)
2. Kia SC176Y, October 2024, Rev 1 of 23 March 2026 — Souls with SC176 done; opened only with P0420; 149 psi minimum. Bulletin (PDF)
3. Kia TSB ENG 160, Rev 1, November 2016 — 2.4 GDI, P0420 during steep downhill engine braking. Bulletin (PDF)
4. Subaru SIB 09-110-23R, revised 7 November 2023 — P0420 diagnostic order and catalyst values. Bulletin (PDF)
5. Honda SB 20-100, 24 November 2020 — 2016 Pilot, software and injectors, 10 years or 150,000 miles. Bulletin (PDF)
6. Honda SB 21-010 owner letter, March 2021 — 2017-2019 Pilot and Ridgeline, 2018-2019 Odyssey injectors. Letter (PDF)
7. Honda SB 18-027, 16 March 2018 — 2015-2016 Fit, false P0420 from injectors. Bulletin (PDF)
8. GM PIP5110C, July 2015 — heavy-duty trucks and vans, leak repair before any converter. PIP (PDF)
9. GM 16-NA-111, March 2019 — V8 air filter seal, debris, P0420 and P0430. Bulletin (PDF)
10. GM 18-NA-331, November 2018 — 2013-2015 Trax and Encore 1.4L software. Bulletin (PDF)
11. GM N212356540 (2019 models) and N222385510 (2021 models, about 158,441 US vehicles) — Traverse and Enclave front exhaust pipe, 15 years or 150,000 miles. N212356540 (PDF) · N222385510 (PDF)
12. Ford emission recall 24E04, October 2024 — 90,892 2022-2023 F-150 hybrids. Bulletin and letter (PDF)
13. Ford TSB 25-2188, 7 May 2025 — 2022-2024 Explorer 2.3L software. Bulletin (PDF)
14. Ford TSB 16-0062, 14 April 2016 — 2012-2015 Focus, fuel gauge and P0420. Bulletin (PDF)
15. Toyota T-SB-0161-13, 31 October 2013 — 2010 Tacoma catalyst rattle, 96 months or 80,000 miles. Bulletin (PDF)
16. Hyundai TSB 20-FL-010H, October 2020 — 2019 Tucson 2.0L manifold catalyst. Bulletin (PDF)
17. 42 U.S.C. 7541(i)(2) — the federal 8-year, 80,000-mile converter warranty. Statute
18. 13 CCR 2037 — California, 7 years or 70,000 miles for high-priced parts. Regulation
19. 40 CFR 85.2222 — OBD inspection and readiness rules. Regulation
20. Our complaint sample — 777,040 unique complaints added 1 January 2015 to 8 September 2026, pulled 14 September 2026. NHTSA complaint file layout

What we looked for and did not find. Volkswagen's 2017 analysis lists name P0420 only on the 2013 Passat 3.6L, with no published fix, so we make no Volkswagen claim. GM's PIP5085 series concerns heavy-duty diesel aftertreatment and does not apply to petrol cars.

Codes and lights: check engine light, flashing light, most expensive codes. Parts: catalytic converter cost, oxygen sensor cost. Symptoms: rattling, gas smell, power loss uphill, noises ranked by cost. Cars and money: Kia Soul, warranty extensions, diagnostic costs, our story.

Methodology. Populations, build windows, remedy logic, labour times and quoted phrases come from the documents above, downloaded and read as text. Complaint counts come from NHTSA's public complaint files, de-duplicated by report number; they are owner reports, not audited repairs. Price ranges are estimates re-checked in September 2026 against published estimator summaries and our cost guides, and are marked ⚪. Eligibility depends on your VIN.

Prices verified: September 2026 · Technical documents verified: September 2026 · Reviewed quarterly

Had P0420 diagnosed, or paid for a converter that did not fix it? Email [email protected] with the year, engine, mileage and what finally cleared the code — owner data is how these ranges get sharper.