P20B9: Reductant (AdBlue) heater A control circuit open or faulty

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.

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 this same explanation and whether it’s confirmed, pending or permanent.

With Free you read this code with its short description for nothing, and clear it if the engine stores it over standard OBD. With Pro you get the full explanation, how the car was running when it was logged (revs, temperature, load) and clearing in every control unit.

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 the ITV. It’s all in how to read and clear fault codes and in the ITV and OBD.

Similar codes

• P2096 Post-catalyst fuel trim system too lean (bank 1)
• P2097 Post-catalyst fuel trim system too rich (bank 1)
• P2098 Post-catalyst fuel trim system too lean (bank 2)
• P2099 Post-catalyst fuel trim system too rich (bank 2)
• P20E8 Reductant (AdBlue) pressure too low
• P20EE SCR NOx catalyst efficiency below threshold (bank 1)
• 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)

P20B9 is a generic code, so it means the same on any make, for example on BMW, Citroën, Ford, Mercedes-Benz, Renault, Volvo. See what Final OBD does on your car in makes and models.