OBD-II code · Powertrain (generic, extended)
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.
Is it safe to drive with P20ED?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyHeater driver shorted on
- PossibleHeater line shorted to positive
- Less likelyCarbon or debris buildup preventing free movement
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)
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Best left to a mechanic
- Typical labour
- 1–4 h
- Emissions test
- Likely to fail
- After the fix
- A drive cycle is needed before the light stays off
- Parts involved
- Reductant Tank Heater, Reductant Dosing Unit
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.