P231C Cylinder 9 Air-Fuel Ratio Imbalance - Adjustment At Limit During Balance
What does P231C mean?
P231C — Cylinder 9 Air-Fuel Ratio Imbalance - Adjustment At Limit During Balance. This is an OBD-II diagnostic trouble code a scanner retrieves when your vehicle's computer detects cylinder 9 air-fuel ratio imbalance - adjustment at limit during balance. The level of risk depends on how the vehicle is currently running and how long you've been driving with the light on.
Common causes of P231C
- Failing ignition coil, spark plug, or spark plug wire
- Faulty crankshaft or camshaft position sensor
- Wiring or connector damage in the ignition circuit
- Low compression or engine mechanical wear
- Incorrect ignition timing or a stretched timing chain
How to fix P231C
These are general steps for this system. The exact cause depends on your vehicle — confirm with live scan data before replacing parts.
- Read misfire counts and freeze frame data with an OBD-II scanner
- Test spark output and inspect spark plugs and coils
- Check crankshaft and camshaft position sensor signals while cranking
- Swap suspect ignition parts between cylinders to see if the fault moves
- Compression test if the issue persists on the same cylinder