P0420: Catalyst System Efficiency Below Threshold (Bank 1)
87 vehicles · 22 makes · $50-$12,000 repair
Most Reported On
P0420 is an OBD-II diagnostic trouble code meaning “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. This code is most commonly reported on 2007-2019 Toyota Tundra (1794 Edition, Base, Limited, Platinum, SR, SR5, TRD Pro), 2017-2023 Honda CR-V (EX, EX-L, Sport, Sport Touring, Sport-L, Touring), and 2004-2012 Mazda RX-8, plus 84 other vehicles, with repair costs ranging from $50 to $12,000.
Common Causes
Typical Repair Cost
Based on 97 documented vehicle-specific issues. Actual cost depends on root cause and vehicle.
Diagnostic Tools
To diagnose P0420, you'll need an OBD-II scanner. Here are our recommendations at every price point.
ANCEL AD310 Classic OBD-II Scanner
by ANCEL
A simple, affordable code reader that reads and clears check engine codes. Great for quick diagnostics on any OBD-II vehicle (1996+).
- Read & clear engine codes
- View freeze frame data
- I/M readiness status
- No batteries or app needed
BlueDriver Pro Bluetooth Scanner
by BlueDriver
Bluetooth OBD-II scanner with a free companion app. Provides enhanced diagnostics, smog readiness, and repair reports sourced from a database of verified fixes.
- Enhanced diagnostics (ABS, SRS, transmission)
- Repair Reports with verified fixes
- Smog check readiness
- Free app (iOS & Android)
LAUNCH CRP123X OBD-II Scanner
by LAUNCH
A professional-grade handheld scanner that reads all four major systems (engine, transmission, ABS, SRS) with live data streaming and graphing.
- Engine, transmission, ABS, SRS diagnostics
- Live data stream & graphing
- AutoVIN for vehicle identification
- Free lifetime updates via Wi-Fi
Autel MaxiCOM MK808S Diagnostic Tool
by Autel
Shop-level diagnostic tablet with bi-directional control, active tests, and full system coverage. Ideal for serious DIYers and small shops.
- All-system diagnostics (25+ modules)
- Bi-directional control & active tests
- Oil reset, EPB, BMS, TPMS, injector coding
- 7-inch touchscreen with Android OS
As an Amazon Associate, we earn from qualifying purchases. Prices are approximate and may vary.
Vehicles Affected (87)
Excessive Oil Consumption (2.4L Piston Ring Defect)
Engine Oil Leak Fire Risk (Oil Filter Adapter)
Persistent Check Engine Light and Electrical System Faults
Excessive Oil Consumption
Oxygen Sensor Failure
Exhaust Manifold Bolt Failure
HEMI Exhaust Manifold Bolt Failure
2.4L MultiAir Excessive Oil Consumption
Plenum Gasket Failure (5.2L/5.9L Magnum V8)
Plenum Gasket Failure (5.2L/5.9L Magnum V8)
Active Exhaust System (AES) Valve Failure
PTU (Power Transfer Unit) Failure
Exhaust Flex Pipe Cracking and Exhaust Leak
Catalytic Converter Efficiency Fault (P0420) on 2.5L Duratec
6.7L Powerstroke Exhaust Manifold Stud Failure
1.5L Turbo Engine Oil Dilution
VCM Oil Consumption and Piston Ring Failure
VCM System Causes Excessive Oil Consumption and Misfires
V6 VCM Excessive Oil Consumption and Engine Vibration
11th Gen Civic Oil Consumption and Honda Sensing Phantom Braking
VCM System - Excessive Oil Consumption and Misfires
Engine Oil Consumption (K24A High Mileage)
VCM System Oil Consumption and Engine Damage
Catalytic Converter Failure (First Gen)
Exhaust Manifold Stud Breakage and Exhaust Leak Tick on 3.2L V6
Excessive Oil Consumption (2.4L Tigershark)
Pentastar V6 Oil Consumption
2.4L Tigershark Oil Pump Failure / Engine Stalling
2.4L Tigershark Excessive Oil Consumption
4.0L Inline-6 Exhaust Manifold Cracking
Exhaust Manifold Bolt Failure and Manifold Leak on 4.7L V8
Catalytic Converter Failure and Pre-Cat Efficiency Codes on 4.0L
Excessive Oil Consumption
Catalytic Converter Overheating and Engine Piston Damage
Nu 2.0L GDI Engine Knocking and Oil Consumption
Premature Catalytic Converter Failure (2.4L GDI)
Piston Oil Ring Defect and Excessive Oil Consumption
Piston Oil Ring Defect and Engine Damage
Catalytic Converter Premature Failure
Exhaust Manifold Bolt Failure and Leak
Excessive Oil Consumption (VQ35DE Engine)
Catalytic Converter Theft Vulnerability
Excessive Oil Consumption (Pre-Revision VQ35DE)
Front Exhaust Flex Pipe / Catalytic Converter Heat Shield Rust and Exhaust Leak Rattle
Engine Oil Leaks (Multiple Locations)
Exhaust Manifold Cracking
Premature Catalytic Converter Failure
Catalytic Converter Premature Failure and Theft
2.5L Pre-Catalyst Breakdown Causing Excessive Oil Consumption and Engine Damage
VQ35DE Rev-Up Engine Oil Consumption
Exhaust Manifold Cracking (Both Banks)
Premature Catalytic Converter Failure
Premature Catalytic Converter Failure
Catalytic Converter Premature Failure (Bank 1)
Rear Main Seal and Valve Cover Oil Leaks
FB25 Engine Excessive Oil Consumption
Excessive Oil Consumption
FB20 Engine Excessive Oil Consumption
Piston Ringland Failure
FB25 Engine Oil Consumption
Catalytic Converter Efficiency Failure (P0420) on Stock Downpipe
Exhaust Manifold Cracking and Bolt Failure
2GR-FE V6 Excessive Oil Consumption
2AR-FE Engine Excessive Oil Consumption
2AZ-FE Engine Excessive Oil Consumption
FA24 Engine Oil Consumption
3rd Generation 2ZR-FXE Excessive Oil Consumption
2GR-FE V6 Excessive Oil Consumption
2.4L 2AZ-FE Excessive Oil Consumption
Pre-Catalytic Converter Disintegration
1ZZ-FE Oil Consumption (MR2 Spyder)
Catalytic Converter Theft Vulnerability
1ZZ-FE Engine Excessive Oil Consumption (GT)
Exhaust Manifold Cracking (4.7L 2UZ-FE V8)
Exhaust Manifold Cracking
2AZ-FE Excessive Oil Consumption from Piston/Ring Wear
Excessive Oil Consumption from 1ZZ-FE Piston Ring Wear
Cracked Exhaust Manifolds on 4.7L V8 Causing Ticking Noise and Exhaust Leaks
Pre-Catalytic Converter Disintegration (Spyder)
FAQ
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 $50 to $12,000, depending on the vehicle and root cause.
Which vehicles are affected by P0420?
Au7o has documented P0420 across 87 vehicle models from 22 manufacturers: BMW, Chevrolet, Chrysler, Dodge, Ford, GMC, Honda, Hyundai, Jeep, Kia, MINI, Mazda, Mercedes-Benz, Nissan, Opel, Peugeot, Porsche, RAM, Subaru, Toyota, Volkswagen, Volvo.
Sources (12)
- mediaClass Action Honda Hid Engine Oil Dilution Defect Newer CR-V - ClassAction
- media2017 Honda CR-V High Oil Level With Gas In Oil - CarComplaints
- mediaHonda Oil Dilution Lawsuit Includes Accord Civic and CR-V - CarComplaints
- mediaValero Law: Class-Action over FCAs Tigershark Oil Consumption Defect
- mediaMyCarVoice: Fiat Chrysler 2.4L Tigershark Engine Class Action Settlement Announced
- ForumJeep Renegade Forum: 2.4L Tigershark Class Action Lawsuit and Oil Consumption Issues
- mediaThe Lemon Firm: Jeep Cherokee 2.4L Tigershark Oil Consumption Causes Engine To Stall
- mediaSauder Schelkopf: Jeep Excessive Engine Oil Consumption Class Action Investigation
- NHTSANHTSA Complaints for 2005 Honda Odyssey - Oil Consumption and Engine Issues
- ForumReddit r/MechanicAdvice Thread Discussing VCM Oil Consumption on Honda Odyssey
- mediaIs Your Subaru Burning Oil - A&A The Shop
- Forum2012 Replacement engine Subaru oil consumption - Subaru Forester Owners
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.