P21A2 code meaning
Cylinder 7 Air-Fuel Ratio Imbalance
Powertrain system Generic code P21xx codes Check engine light
What P21A2 means
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.
P21A2 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 6 hours
- Clears after repairAfter a drive cycle
Symptoms of P21A2
- Check engine light on
- Often no noticeable symptom
- Possible P0307 if the deviation is large
Common causes of P21A2
- Most likelyCylinder 7 injector clogged or leaking
- PossibleIntake runner or injector seal leak at cylinder 7
- Less likelyCompression loss at cylinder 7
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Fuel injector
What each part of P21A2 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 1 | Area: fuel and air metering. |
| A2 | The exact fault in that area. |
What to do next
- Note P21A2 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P21A2
What does P21A2 mean?
P21A2 means "Cylinder 7 Air-Fuel Ratio Imbalance". P21A2 places a mixture imbalance at cylinder 7, so it only exists on engines with eight or more cylinders. It is a generic code, so it means the same on every make.
Is it safe to drive with P21A2?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P21A2 fail an emissions test?
Yes, it can. P21A2 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P21A2 to fix?
Difficulty: medium. A typical repair takes 0.5 to 6 hours of work. This is a job for a workshop.
Will P21A2 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.