OBD-II code · Powertrain (generic, extended)
P21C6 Reductant Level Sensor B Stuck
DEF level sensor B reading does not change over a refill or consumption window — float arm jammed or sender wiper stuck. Distinct from a circuit fault because the electrical signal stays plausible.
Is it safe to drive with P21C6?
Usually safe for short trips, but don’t ignore it: the underlying fault can get more expensive over time.
Common causes
- Most likelyFloat arm jammed
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
- Hard
- DIY friendly
- Best left to a mechanic
- Typical labour
- 1–4 h
- Emissions test
- Likely to fail
- Parts involved
- Reductant Level Sensor
Related codes
- P21C5Reductant Level Sensor A Stuck
- P21C3Reductant Heater Relay Control Circuit Low
- P21C4Reductant Heater Relay Control Circuit High
- P21C7Reductant Control Module Power Relay Control Circuit/Open
- P21C8Reductant Control Module Power Relay Control Circuit Low
- P21C9Reductant Control Module Power Relay Control Circuit High
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.