OBD-II code · Powertrain (generic, extended)
P20BB Reductant Heater A Control Circuit Low
Reductant heater A control line stuck low — short to ground. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.
Is it safe to drive with P20BB?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyShort to ground
- Less likelyConnector pins corroded - high contact resistance
- Less likelyHarness chafing through insulation
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
- P20B9Reductant Heater A Control Circuit/Open
- P20BFReductant Heater B Control Circuit Low
- P20C3Reductant Heater C Control Circuit Low
- P20C7Reductant Heater D Control Circuit Low
- P20B8Reductant Metering Unit Heater Control Circuit High
- P20BAReductant Heater A Control Performance
- P20BCReductant Heater A Control Circuit High
- P20BDReductant Heater B Control Circuit/Open
- P20BEReductant Heater B Control Circuit Performance
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.