OBD-II code · Powertrain (generic, extended)
P21AC Reductant Level Sensor B Circuit Intermittent/Erratic
Reductant Level Sensor B 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 P21AC?
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
- P21B1Reductant Level Sensor C Circuit Intermittent/Erratic
- P21A9Reductant Level Sensor B Circuit Range/Performance
- P21AAReductant Level Sensor B Circuit Low
- P21ABReductant Level Sensor B Circuit High
- P21ADReductant Level Sensor C Circuit
- P21AEReductant Level Sensor C Circuit Range/Performance
- P21AFReductant Level Sensor C Circuit Low
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.