P0420: How to Diagnose & Fix — Catalyst System Efficiency Below Threshold (Bank 1)
97 vehicles · 29 makes · $40-$12,000 repair
How to diagnose and fix P0420: most-reported vehicles
Ranked by owner reports. Each card gives the symptoms, how to confirm the cause, the fix, parts and sources for that vehicle.
Toyota Tundra · 2007–2019
Toyota Tundra V8 engines are prone to exhaust manifold cracking, particularly on the driver side where the air injection tube weld enters the manifold. Additionally, exhaust manifold bolts can corrode and break, causing exhaust leaks. The ticking noise is most noticeable at cold startup.
Common Symptoms
- Ticking noise at cold startup
- Exhaust smell in cabin
- Hissing sound from engine bay
- Reduced fuel economy
- Failed emissions test
How to Fix
Repair options include welding cracks (temporary), replacing with OEM manifolds ($800-$1,500), or upgrading to aftermarket headers ($1,000-$2,500). Broken bolts require extraction. Total repair costs range from $500 to $3,000+.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Toyota 17104-50220 genuine right exhaust manifold
replace a test-confirmed cracked or warped right 4.7L exhaust manifold Fitment/availability: Right-side 4.7L 2UZ-FE Tundra branch; use only after VIN, engine, production date, emissions and secondary-air configuration are confirmed Fitme…
- Toyota 17105-50210 genuine left exhaust manifold
replace a test-confirmed cracked or warped left 4.7L exhaust manifold Fitment/availability: Left-side 4.7L 2UZ-FE Tundra branch; use only after VIN, engine, production date, emissions and secondary-air configuration are confirmed Fitment…
- Toyota 17104-38011 genuine right exhaust manifold
replace a test-confirmed cracked or warped right 5.7L exhaust manifold Fitment/availability: Right-side 5.7L 3UR-FE/3UR-FBE branch; the page supersedes 17104-38010 to 17104-38011, and VIN, emissions and secondary-air configuration still …
- Toyota 17105-38011 genuine left exhaust manifold
replace a test-confirmed cracked or warped left 5.7L exhaust manifold Fitment/availability: Left-side 5.7L 3UR-FE/3UR-FBE branch; the page supersedes 17105-38010 to 17105-38011, and VIN, emissions and secondary-air configuration still re…
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Owner tips & cautions
- TipDIY repairs can save significantly - dealer charges $800-$1,500 but DIY costs are typically 50-70% less
- TipConsider OEM parts for critical components like sensors and electrical parts - aftermarket can be unreliable
- TipGet a proper diagnosis before replacing parts - similar symptoms can have different causes
Sources for this issue (1)
Honda CR-V · 2017–2023
Gasoline mixes with engine oil in the 1.5L turbocharged engine, causing the oil level to rise above the full mark. The issue is most prevalent in cold climates where short trips don't allow the engine to reach full operating temperature. Unburned fuel bypasses the piston rings and enters the crankcase, diluting the oil and reducing its lubricating properties.
Common Symptoms
- Oil level reading above full mark on dipstick
- Strong gasoline smell from engine oil
- Check engine light illumination
- Reduced engine power
- Engine stalling
- Poor fuel economy
How to Fix
Honda released a software update for the engine and transmission control units (with an oil change, and in some cases a replacement A/C control unit) to help the engine warm up faster in cold conditions. For 2017-2018 models, Honda also extended warranty coverage on the camshaft, rocker-arm assemblies and spark plugs by one year, to 6 years from purchase with unlimited miles. Owners should change oil more frequently (every 3,000-5,000 miles) in cold climates.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Genuine Honda 15400-PLM-A02 engine oil filterOEMHonda 15400-PLM-A02
Oil-filter consumable when an owner performs the shorter oil-change interval described by the repair guidance Fitment/availability: 2017-2023 U.S. CR-V 1.5T within this record; cataloged broadly for the CR-V and shown specifically for th…
Owner tips & cautions
- WarningThis is a high-severity issue - ignoring it can lead to costly repairs or safety concerns. Address it promptly.
- TipGet a proper diagnosis before replacing parts - similar symptoms can have different causes
- TipSearch Honda CR-V forums and owner groups for real-world experiences and DIY guides
- TipGet multiple quotes from independent mechanics - dealer prices can be 2-3x higher for the same repair
Sources for this issue (4)
Jeep Cherokee · 2014–2019
The 2.4L Tigershark MultiAir engine suffers from defective piston rings allowing oil to burn in combustion chamber. Owners report consuming 1 quart per 1,000 miles. Engine can stall when oil falls below 3.5 quarts without warning light.
Common Symptoms
- Consuming 1+ quart of oil every 1,000-2,000 miles
- Engine stalling without warning
- Oil light only after engine stalls
- Blue smoke from exhaust during acceleration
- Rough idle or misfires
How to Fix
FCA Warranty Extension XB1 covers excessive oil consumption for 7 years/100,000 miles. Engine recalibration/PCM software update can reduce consumption. Severe cases require engine replacement or rebuild with updated piston rings.
Owner tips & cautions
- WarningCheck oil level every 500-1,000 miles religiously
- TipDocument oil consumption with receipts for warranty claims
Sources for this issue (5)
- Valero Law: Class-Action over FCAs Tigershark Oil Consumption Defectmedia
- MyCarVoice: Fiat Chrysler 2.4L Tigershark Engine Class Action Settlement Announcedmedia
- Jeep Renegade Forum: 2.4L Tigershark Class Action Lawsuit and Oil Consumption Issuesforum
- The Lemon Firm: Jeep Cherokee 2.4L Tigershark Oil Consumption Causes Engine To Stallmedia
- Sauder Schelkopf: Jeep Excessive Engine Oil Consumption Class Action Investigationmedia
Mazda RX-8 · 2004–2012
Honda Odyssey · 2005–2017
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P0420 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0420 mean?
P0420 stands for "Catalyst System Efficiency Below Threshold (Bank 1)." P0420 means the engine computer determined the catalytic converter on Bank 1 isn't cleaning the exhaust as efficiently as it should. The computer compares the upstream and downstream oxygen sensors; a healthy converter stores and releases oxygen, so the downstream sensor should read fairly steady, while a worn one lets its readings mirror the upstream sensor. When that efficiency falls below a set threshold, this code is set. While it most often points to a worn-out catalytic converter, it can also be triggered by upstream problems like a faulty oxygen sensor or an exhaust leak, so the converter isn't always the actual fault.
What are the most common causes of P0420?
The most common causes of P0420 are: Worn-out or failing catalytic converter (Bank 1), Faulty or aged downstream (or upstream) oxygen sensor, Exhaust leak before or near the oxygen sensors, Engine running rich or lean (fuel trim issues), Misfires or oil/coolant contaminating the converter, Damaged or aftermarket low-quality catalytic converter, Faulty oxygen sensor wiring or connectors, Software/calibration needing update (on some vehicles). The specific cause varies by vehicle.
How much does it cost to fix P0420?
Repair costs for P0420 range from $40 to $12,000, depending on the vehicle and root cause.
Which vehicles are affected by P0420?
Au7o has documented P0420 across 97 vehicle models from 29 manufacturers: Acura, Alfa Romeo, Audi, BMW, Buick, Cadillac, Chevrolet, Chrysler, Dodge, Ford, GMC, Honda, Hyundai, Infiniti, Jeep, Kia, MINI, Mazda, Mercedes-Benz, Mitsubishi, Nissan, Opel, Peugeot, Porsche, RAM, Subaru, Toyota, Volkswagen, Volvo.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.