P21A9: The AdBlue level sensor B gives readings outside the normal range
The AdBlue level sensor B gives readings outside the normal range. It is usually the sensor itself, its wiring or a real fault in what it measures.
| Code | P21A9 |
|---|---|
| System | Engine and transmission |
| Group | P21xx, Throttle, injection and emissions |
| Type | Generic: it means the same on every make |
How to read and clear P21A9 with Final OBD
Plug an OBD2 scanner in under the steering wheel, switch the ignition on and open Final OBD. Under Faults you’ll see P21A9 with its description and whether it’s confirmed, pending or permanent.
If the engine stores it over standard OBD, with FREE you read this code with its explanation for nothing and clear it. With PRO you also read the faults of every control unit and clear them in all of them.
Clearing the code only turns the light off: if the cause is still there, it comes back. Clear it once it’s fixed, and not right before an inspection. It’s all in how to read and clear fault codes and in inspections and OBD.
Similar codes
- P21A5 Cylinder 10 is getting a different mixture from the others
- P21A6 Cylinder 11 is getting a different mixture from the others
- P21A7 Cylinder 12 is getting a different mixture from the others
- P21A8 The AdBlue level sensor B has an electrical fault
- P21AA The AdBlue level sensor B gives a lower signal than normal
- P21AB The AdBlue level sensor B gives a higher signal than normal
- P21AC The AdBlue level sensor B fails now and then
- P21AD The AdBlue level sensor C has an electrical fault
- P2100 Throttle actuator A control motor circuit open
- P2101 Throttle actuator A control motor circuit range or performance
- P2102 Throttle actuator A control motor circuit low
- P2104 Throttle control system: forced idle
What does code P21A9 mean?
The AdBlue level sensor B gives readings outside the normal range. It is usually the sensor itself, its wiring or a real fault in what it measures.
How do you clear P21A9?
With an OBD2 scanner and an app like Final OBD, which clears it for free if it’s stored by the engine control unit. But clearing it only turns the light off: if the cause isn’t fixed, P21A9 comes back.
Read it on your car
Final OBD reads and clears engine faults through standard OBD for free, each one explained in plain English. With PRO it also reads the faults of every control unit, each make’s own codes included, and clears them in all of them.
