P21A6Cylinder 11 Air-Fuel Ratio Imbalance
- 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
- P21A6 assigns the imbalance to cylinder 11, which exists only on twelve-cylinder engines. No manufacturer has published how it detects this code, and no NHTSA bulletin names it, so it is a placeholder that J2012 provides for large engines. The legal frame is CARB's cylinder imbalance monitor (13 CCR 1968.2 (e)(6.2.1)(C)). A V12 or W12 feeds six cylinders into each front sensor, and exhaust pulses overlap, which makes a clean per-cylinder reading hard; the Cummins patent describes estimating the signal content at the engine cycle frequency and then trimming the fuel of the cylinder that causes it, an approach suited to many cylinders. In practice the work is mechanical: confirm the numbering, compare injector delivery across the bank and run a compression or leak-down test on cylinder 11.
- What you may notice
- Check engine light on
- Possible P0311 with a large deviation
- Likely causes
- LikelyCylinder 11 injector clogged or leaking
- PossibleValve leakage at cylinder 11
- RareIntake leak at cylinder 11
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €0 – €3,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.