P231BCylinder 8 Air-Fuel Ratio Imbalance - Adjustment At Limit During Balance
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- P231B is the balance-limit code for cylinder 8, the last cylinder of a V8 and an inner one on V10 and V12 engines. The fuel trim for that cylinder has hit its stop while balancing. No maker documents P231B publicly; the nearest evidence is Mercedes' bulletin for the AMG M177 V8 in the SL, which shows that this engine uses the cylinder 7 to 12 range and treats it partly as a software issue, together with CARB's rule that the stored code should locate the cause as precisely as the method allows. On a V8, cylinder 8 shares a bank with three others, so cross-check the bank code P219A or P219B, the misfire counter P0308 and the imbalance code P21A3. Injector 8, the intake gasket and compression come next.
- What you may notice
- Check engine light on
- Rough idle, possibly misfire on cylinder 8
- Higher fuel consumption or exhaust smell
- Likely causes
- LikelyInjector of cylinder 8 delivering too much or too little (deposits, wear)
- PossibleAir leak at the intake port or injector seal of cylinder 8
- PossibleValve of cylinder 8 not sealing (worn seat or guide), low compression
- RarePoor contact at the connector of injector 8
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €0 – €1,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.