P20B9
PPowertrainReductant (AdBlue) Heater A Control Circuit/Open
What does this code mean?
Severity : MediumP20B9 indicates an open or fault in the control circuit of reductant heater A, which keeps AdBlue/DEF from freezing. AdBlue freezes at around minus 11 °C, so the heater is needed in cold weather. The ECU detects an electrical problem on this circuit and can no longer guarantee the system will work in the cold.
Symptoms
- AdBlue or check engine light on.
- Warning message with a countdown before engine start is restricted.
- AdBlue dosing problems in cold weather.
- No noticeable symptom in mild weather.
Possible causes
- Open AdBlue heating element.
- Corroded connector or damaged pins.
- Broken or chafed wiring.
- Faulty heater supply fuse or relay.
- Less commonly, an SCR control unit fault.
Diagnosis and repair
- Inspect the AdBlue heater connector and wiring.
- Check the supply fuse and relay.
- Measure heating element resistance and compare it to the manufacturer's values.
- Repair the wiring or replace the heater, often built into the tank module or line.
- Clear the code and check operation with a diagnostic tool.
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Code
P20B9
Category
Powertrain
Prefix
P
Standard
OBD-II / SAE J2012