OBD-II code · Powertrain (generic, extended)
P21DD Reductant Heater A Current Too Low
DEF heater A current draw is below threshold — partially-open winding.
Is it safe to drive with P21DD?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyElement partially open
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
- 0.7–3 h
- Emissions test
- Likely to fail
- Parts involved
- Reductant Line Heater A
Related codes
- P214FReductant Heater A Current Too High
- P215EReductant Heater D Current Too Low
- P221CReductant Heater B Current Too Low
- P221EReductant Heater C Current Too Low
- P21DACylinder 12 Injector B Circuit/Open
- P21DBCylinder 1 Injector B Circuit Low
- P21DCCylinder 1 Injector B Circuit High
- P21DECylinder 2 Injector B Circuit Low
- P21DFCylinder 2 Injector B Circuit High
- P21E0Cylinder 3 Injector B Circuit Low
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.