P21A2Cylinder 7 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
- P21A2 places a mixture imbalance at cylinder 7, so it only exists on engines with eight or more cylinders. No manufacturer documents this code publicly; the bulletin index of the US safety authority NHTSA contains no bulletin that names it. The requirement behind it is CARB's monitor for uneven mixture between cylinders (13 CCR 1968.2 (e)(6.2.1)(C)), which asks the code to identify the cause as far as the method allows. A V8 has four cylinders per front sensor, so the sensor signal alone separates them less clearly than on a four-cylinder; methods that work at the engine cycle frequency, as described in a Cummins patent, or VW's individual leaning test make cylinder-level codes possible. Check the cylinder 7 injector, its intake sealing and compression, and compare with misfire counts.
- What you may notice
- Check engine light on
- Often no noticeable symptom
- Possible P0307 if the deviation is large
- Likely causes
- LikelyCylinder 7 injector clogged or leaking
- PossibleIntake runner or injector seal leak at cylinder 7
- RareCompression loss at cylinder 7
- 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.