P21A7Cylinder 12 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
- P21A7 is the last code of the cylinder series that starts with P219C and points to cylinder 12 of a twelve-cylinder engine. There is no public manufacturer description and no NHTSA bulletin for it. Under CARB's rule (13 CCR 1968.2 (e)(6.2.1)(C)) the monitor had to be in all 2014 and later petrol vehicles, with limits of 3.0 times the FTP standard until 2014 and 1.5 times from 2015 for non-LEV III cars, so twelve-cylinder engines are covered as well; many simply report the bank code P219A or P219B. The causes do not differ from smaller engines: a single injector, a leaking intake seal or a valve that does not close properly. Because a V12 has two separate banks, check whether the bank code and the misfire counter P0312 agree with cylinder 12 before parts are replaced.
- What you may notice
- Check engine light on
- Possible P0312 or slight vibration
- Likely causes
- LikelyCylinder 12 injector out of tolerance
- PossibleIntake seal leak at cylinder 12
- RareValve not sealing at cylinder 12
- 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.