OBD-II code · Powertrain (generic, extended)
P21B1 Reductant Level Sensor C Circuit Intermittent/Erratic
Reductant Level Sensor C Circuit Intermittent/Erratic: the signal is intermittent or erratic. Often a loose connector or chafed wiring; a wiggle test often locates it.
Is it safe to drive with P21B1?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyCorroded sender contact
- Less likelyConnector with intermittent contact under vibration
- Less likelyHarness routed against vibrating component
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 Level Sensor
Related codes
- P203EReductant Level Sensor A Circuit Intermittent/Erratic
- P21ACReductant Level Sensor B Circuit Intermittent/Erratic
- P21AEReductant Level Sensor C Circuit Range/Performance
- P21AFReductant Level Sensor C Circuit Low
- P21B0Reductant Level Sensor C Circuit High
- P21B2Excessive Time To Enter Closed Loop NOx Adsorber Control
- P21B3Closed Loop NOx Adsorber Control At Limit - Too High
- P21B4NOx Adsorber Over Temperature (Bank 1)
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.