Your check-engine light is on. Here's what the code means.
Type the code from your scanner or auto-parts-store printout — for example, P0420 — and get a plain-English explanation: what it means, what it means for driving, the symptoms, the most likely causes, and the likely fixes.
Important: CheckMyCarCode is general information only — not professional mechanical advice and not a diagnosis for your specific vehicle. Fault causes and severity vary by make, model, year, and condition. When in doubt, have a qualified mechanic assess it promptly, and if you notice a red-flag symptom (flashing check-engine light, loss of power, overheating, strange noises or smells), stop driving and arrange a tow.
Most common codes
Your car's computer has decided the catalytic converter on bank 1 (the side of the engine containing cylinder 1) is no longer cleaning exhaust gases as effectively as it should.
The engine computer has detected misfires happening across multiple cylinders rather than one specific cylinder — the engine is not firing cleanly on all cylinders.
Bank 1 of the engine is running lean — there is too much air, or too little fuel, in the air-fuel mixture compared with what the computer expects.
The evaporative emissions (EVAP) system, which traps fuel vapors from the tank instead of venting them, has a large leak — the system cannot hold pressure during its self-test.
The catalytic converter on bank 2 (the side of the engine opposite cylinder 1, on V6/V8 engines) is no longer cleaning exhaust gases as effectively as it should. It is the bank-2 twin of P0420.
The engine is not reaching its normal operating temperature within the expected time — the coolant is staying cooler than the thermostat is designed to allow.
Bank 2 of the engine is running lean — too much air, or too little fuel, in the mixture. It is the bank-2 twin of P0171, seen on V6/V8 engines.
The EVAP system, which traps fuel vapors instead of venting them, has a small leak — it cannot quite hold pressure during its self-test.
Browse by system
One or more cylinders not firing cleanly — rough idle, shaking, hesitation. (7 codes so far)
Catalytic converter, EGR, and exhaust aftertreatment faults. (3 codes so far)
Too lean or too rich — the air-fuel mixture is off. (3 codes so far)
Fuel-vapor leaks, from a loose gas cap to a faulty valve. (2 codes so far)
Camshaft, crankshaft, and vehicle-speed sensor faults. (3 codes so far)
Transmission control faults, harsh shifting, and limp mode. (1 code so far)
Thermostat and coolant-temperature faults. (1 code so far)
How to get your code
- Free: most auto-parts stores will read your codes free with a handheld scanner.
- DIY: a basic OBD-II Bluetooth scanner pairs with a free phone app.
- At a shop: a mechanic can run a full diagnostic scan; ask whether the fee is credited toward the repair.
Note the exact code (a letter followed by four digits, like P0420) and type it above — or browse all codes.