Car trouble codes, explained plainly
Pick the fault group that matches your check-engine code. Each guide covers what the code means, how serious it is, the common causes and the first checks to make. SmartChecker then reads the code and the live data behind it for free, with no subscription.
Engine misfire codes
A cylinder isn't burning its fuel–air charge cleanly.
Lean fuel mixture codes
The engine is running with too much air for the fuel it's getting.
Rich fuel mixture codes
The engine is getting more fuel than it needs.
Catalytic converter efficiency codes
The converter isn't cleaning the exhaust as well as it should.
Mass air flow (MAF) sensor codes
The sensor that measures incoming air is reading wrong.
Throttle & pedal position codes
The electronic throttle or accelerator-pedal signal is out of range.
Coolant temperature & thermostat codes
The engine isn't reaching or holding its normal operating temperature.
EVAP (evaporative emissions) leak codes
The system that traps fuel vapour has a leak or a stuck valve.
Oxygen (O2) sensor codes
An oxygen sensor's signal is slow, stuck or out of range.
Camshaft / crankshaft timing (VVT) codes
Valve timing or the cam/crank correlation is off.
Charging system & system voltage codes
System voltage is too low or too high.
Lost communication (CAN bus) codes
A module has stopped talking on the vehicle network.
Diagnose it yourself with SmartChecker
SmartChecker is a Windows scan tool that reads codes, live data, freeze frames and readiness on 1996-and-newer vehicles for free — no subscription. A one-time license adds the tests that control the vehicle, clearing codes, module programming and the Head Tech: an AI that runs on your own PC and explains what the data means. It's in beta now: join the waitlist to get it.