Skip to contentGarageFix
Plans and pricingFor mechanics
Sign in
← All fault codes

OBD-II · Engine and powertrain (P)

P20B9

AdBlue heater A control circuit/open

What it means

AdBlue freezes at about -11 C, so the tank and lines have heaters. The engine computer sees an electrical fault (open circuit) in heater A, usually the tank heater; the exact heater depends on the car.

Symptoms

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

Likely causes, most likely first

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

What to check, step by step

  1. 01Check the fuse and relay for the AdBlue heaters.
  2. 02Inspect the tank connector for corrosion (it is exposed to road spray).
  3. 03Measure heater resistance at the connector and compare with specification.
  4. 04Replace the tank module or heater if open circuit.