OBD-II Fault Code Guides
Mechanic-written repair guides for every trouble code — what it really means, what actually causes it, and how to fix it before you replace expensive parts.
Every code is four signals in five characters.
Powertrain
Engine, fuel, ignition, emissions and transmission. By far the most common — most check-engine lights start with P.
Body
Interior comfort and safety: airbags, lighting, power windows, seats, climate control.
Chassis
Mechanical systems outside the body: ABS, traction control, steering, suspension, wheel-speed sensors.
Network
Communication between control modules over the car's data bus (CAN). Often points to wiring or a module that has gone quiet.
Generic vs manufacturer-specific: a 0 in the second position means the code follows the SAE standard and means the same on every car — those are the ones in this library. A 1 (and sometimes 3) means the carmaker defined it themselves, so the same code can mean different things on a BMW and a Toyota. For those, read the exact definition on your scan tool.
Four moves, in order.
Is it flashing?
A flashing check-engine light usually means an active misfire that can damage the catalytic converter — ease off the throttle and get it looked at promptly. A steady light is rarely an emergency; investigate soon.
Scan for the codes
Plug in a scan tool and read the stored codes. Note every code and its freeze-frame data — the first one set is often the root cause of the rest.
Look it up
Search the code here to understand what system it points to, how serious it is, and the parts most often behind it — before you spend a cent on parts.
Fix, clear, confirm
Repair the root cause, clear the code, then drive and re-scan. If it comes straight back, the underlying fault is still there — keep diagnosing, don't just keep clearing.
A code tells you the system. A scanner tells you the part.
Reading the code is step one. ICARZONE tools go further — live data, bidirectional actuator tests and OE-level access pinpoint the actual faulty component, then clear the code once it's fixed.
Can't find your code, or got a P1/B1/C1/U1 code? Those are manufacturer-specific. Tell our team the code and your vehicle (make, model, year) and we'll help you read it — or grab the exact OE definition with an ICARZONE tool. Contact support →