P20B9: Reductant (AdBlue) heater A control circuit open or faulty
The ECU cannot control the heater that stops AdBlue from freezing. Usually a connector, wire, fuse or the heater element itself.
| Code | P20B9 |
|---|---|
| System | Engine and transmission |
| Group | P20xx, Emissions: catalysts and AdBlue |
| Type | Generic: it means the same on every make |
| Can you keep driving? | With care |
What P20B9 means
AdBlue freezes at around minus 11 degrees Celsius, so the tank, pump and sometimes the lines have heating elements. The ECU has detected an open circuit or electrical fault on heater A. Whether A is the tank, pump or line heater is set by each manufacturer.
Most common causes
- Heater connector loose, dirty or corroded
- Broken or damaged wire, often under the car
- Blown heater fuse or failed relay
- Failed heating element (sometimes built into the tank module)
- Control module fault (uncommon)
Symptoms
- Engine warning light on
- AdBlue warning on the dashboard
- In cold weather the AdBlue system may stop working
- Possible countdown before the engine is prevented from starting
Can you drive with P20B9?
With care You can drive, but get it fixed soon, especially before winter. On many cars, if the fault persists, a dashboard message counts down the distance left before the engine will not restart.
Open the bonnetthe in-depth explanation
How to check it
Find the AdBlue heater fuse in the owner’s handbook and check it. Inspect the connector on the AdBlue tank module, which is often exposed to water and road salt underneath.
How to read and clear P20B9 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 P20B9 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
- P20B5 The AdBlue metering unit heater control has a broken or disconnected wire
- P20B6 The AdBlue metering unit heater control gives readings outside the normal range
- P20B7 The AdBlue metering unit heater control gives a lower signal than normal
- P20B8 The AdBlue metering unit heater control gives a higher signal than normal
- P20BA The AdBlue heater A control gives readings outside the normal range
- P20BB The AdBlue heater A control gives a lower signal than normal
- P20BC The AdBlue heater A control gives a higher signal than normal
- P20BD The AdBlue heater B control has a broken or disconnected wire
- P2002 Diesel particulate filter efficiency below threshold (bank 1)
- P2003 Diesel particulate filter efficiency below threshold (bank 2)
- P2004 Intake manifold runner control stuck open (bank 1)
- P2005 Intake manifold runner control stuck open (bank 2)
To understand it properly
We explain how that system works, with drawings and no waffle, in our mechanics guide: AdBlue.
What does code P20B9 mean?
AdBlue freezes at around minus 11 degrees Celsius, so the tank, pump and sometimes the lines have heating elements. The ECU has detected an open circuit or electrical fault on heater A. Whether A is the tank, pump or line heater is set by each manufacturer.
Can you drive with P20B9?
You can drive, but get it fixed soon, especially before winter. On many cars, if the fault persists, a dashboard message counts down the distance left before the engine will not restart.
How do you clear P20B9?
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, P20B9 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.
