P21A0 code meaning
Cylinder 5 Air-Fuel Ratio Imbalance
Powertrain system Generic code P21xx codes Check engine light
What P21A0 means
P21A0 can only occur on engines with at least five cylinders. VW's 2014 specification books for the Golf, Jetta, Passat and Beetle with the 2.5 litre inline five list P219C to P21A0, one per cylinder, all judged the same way: the ECM briefly leans one cylinder, measures how much rougher the engine runs and derives an individual fuel correction; a result below 0.19 or above 1.50 is a fault. On a five-cylinder with a single front sensor, the bank code P219A belongs to the same engine. Six-cylinder users include Toyota's 2015 Tacoma 1GR-FE, Audi's 3.0 TFSI (software) and Kia's 2022 Carnival 3.5 GDI (injectors). Because the method uses roughness, a weak ignition coil or a compression problem in cylinder 5 can also influence the result.
P21A0 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 5 hours
- Clears after repairAfter a drive cycle
Symptoms of P21A0
- Check engine light on
- Possible P0305 or slight vibration at idle
Common causes of P21A0
- Most likelyCylinder 5 injector out of tolerance
- PossibleIgnition or compression weakness at cylinder 5 affecting the roughness test
- Less likelySoftware setting corrected by an update (e.g. Audi 3.0 TFSI)
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 P21A0 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. |
| A0 | The exact fault in that area. |
What to do next
- Note P21A0 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 P21A0
What does P21A0 mean?
P21A0 means "Cylinder 5 Air-Fuel Ratio Imbalance". P21A0 can only occur on engines with at least five cylinders. It is a generic code, so it means the same on every make.
Is it safe to drive with P21A0?
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 P21A0 fail an emissions test?
Yes, it can. P21A0 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 P21A0 to fix?
Difficulty: medium. A typical repair takes 0.5 to 5 hours of work. This is a job for a workshop.
Will P21A0 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.