P20BA
Reductant Heater A Control Performance
The reductant (AdBlue/DEF) tank or line heater A does not reach the expected temperature within the calibrated time window. In cold weather frozen DEF blocks the SCR dosing system and the engine enters a no-restart state after ignored warnings.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: hard
Symptoms
- Check engine light or NOx warning on
- AdBlue/DEF level or quality warning
- Possible no-start countdown after ignore period
- Failed emissions inspection (NOx)
Common causes
Ordered by how often each turns out to be the cause.
- Heater element failedCommon
- Tank temperature sensor driftPossible
- Heater relay failedLess likely
Parts involved
- Reductant Tank Heater
- Reductant Line Heater
- Reductant Temperature Sensor
P20BA is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.