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EmissionsSeverity Medium: diagnose soon

P20B9Reductant Heater "A" Control Circuit/Open

What it means

The ECU sees an open circuit in the AdBlue heater circuit. In cold weather AdBlue can freeze and dosing stops.

Symptoms

  • AdBlue or emissions warning
  • Countdown to a no-restart condition on many cars
  • Usually no change in power until the countdown ends

Common causes

  • Failed heater element (often part of the tank unit)
  • Open wiring or blown fuse
  • Control module fault

What to check first

  1. Measure the heater resistance
  2. Check fuse and supply
  3. Check the connector on the tank unit
Can I drive with P20B9? Usually yes for a short distance, but performance or economy may suffer and the fault can get worse. Diagnose it soon.

Generic OBD-II meaning. Manufacturer-specific meanings and checks can differ; always check the service information for the car.

Cases with P20B9 (0)

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P20B9: questions and answers

What does P20B9 mean?

P20B9: Reductant Heater "A" Control Circuit/Open. The ECU sees an open circuit in the AdBlue heater circuit. In cold weather AdBlue can freeze and dosing stops.

What are the symptoms of P20B9?

AdBlue or emissions warning. Countdown to a no-restart condition on many cars. Usually no change in power until the countdown ends.

What causes P20B9?

Failed heater element (often part of the tank unit). Open wiring or blown fuse. Control module fault.

How do you diagnose P20B9?

1. Measure the heater resistance 2. Check fuse and supply 3. Check the connector on the tank unit

Can I drive with P20B9?

Usually yes for a short distance, but performance or economy may suffer and the fault can get worse. Diagnose it soon.