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OBD-II · Engine and powertrain (P)

P20BD

AdBlue heater B control circuit/open

What it means

The engine computer sees an electrical fault (open circuit) in AdBlue heater B. Which heater this is (often the supply line or pump heater) depends on the car.

Symptoms

  • AdBlue/emissions warning, possibly with a no-start countdown
  • AdBlue system may fail in cold weather

Likely causes, most likely first

Likely causes, most likely first
No.Cause
01failed heater in the AdBlue line or pump
02corroded connector
03wiring damage under the car
04fuse or relay fault

What to check, step by step

  1. 01Identify heater B from the wiring diagram for the car.
  2. 02Check fuse and relay.
  3. 03Inspect and measure the heater circuit resistance.
  4. 04Replace the heated line or pump module if open circuit.