P20ED
Reductant Heater "A" Control Stuck On
The reductant tank heater "A" stays energised even when not commanded — usually a shorted driver stage. Continuous heating wastes current and can overheat the heater element.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
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 driver shorted onCommon
- Heater line shorted to positivePossible
- Carbon or debris buildup preventing free movementLess likely
Parts involved
- Reductant Tank Heater
- Reductant Dosing Unit
P20ED 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.