OBD-II code · Powertrain (generic, extended)
P20B9 Reductant Heater A Control Circuit/Open
Reductant heater A (typically the supply line heater nearest the tank) control circuit is open — that segment of DEF line will not be kept above freezing in winter.
Is it safe to drive with P20B9?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyHeater winding open
- Less likelyPin pushed back out of connector body
- Less likelyCracked solder joint inside the module or sensor
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
- P20BDReductant Heater B Control Circuit/Open
- P20C1Reductant Heater C Control Circuit/Open
- P20C5Reductant Heater D Control Circuit/Open
- P20B6Reductant Metering Unit Heater Control Circuit Performance
- P20B7Reductant Metering Unit Heater Control Circuit Low
- P20B8Reductant Metering Unit Heater Control Circuit High
- P20BAReductant Heater A Control Performance
- P20BBReductant Heater A Control Circuit Low
- P20BCReductant Heater A Control Circuit High
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.