OBD-II code · Powertrain (generic, extended)
P21B0 Reductant Level Sensor C Circuit High
DEF level sensor C reads above upper plausibility — open signal or short to B+. 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 P21B0?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyOpen signal line
- Less likelyConnector pins corroded - high contact resistance
- Less likelySupply wire pinched against B+ source
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
- P203DReductant Level Sensor A Circuit High
- P21ABReductant Level Sensor B Circuit High
- P21ADReductant Level Sensor C Circuit
- P21AEReductant Level Sensor C Circuit Range/Performance
- P21AFReductant Level Sensor C Circuit Low
- P21B1Reductant Level Sensor C Circuit Intermittent/Erratic
- P21B2Excessive Time To Enter Closed Loop NOx Adsorber Control
- P21B3Closed Loop NOx Adsorber Control At Limit - Too High
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.