Powertrain
generic / SAE
P21AC
Reductant Level Sensor B Circuit Intermittent/Erratic
DEF level sensor B signal jumps or drops out intermittently — typically a corroded sender contact or wiring issue.
SystemPowertrain
Typegeneric / SAE
GroupP2
Range / number1 / AC
Possible causes
- Corroded sender contact high
- Connector with intermittent contact under vibration low
- Harness routed against vibrating component low
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)
Inspection / repair
- Difficulty: medium
- DIY: shop recommended
- Estimated cost: 60–600 €
- Estimated time: 0.7–3 h
- Component: reductant level sensor
- MIL / check engine light
- emissions-relevant
Sources
References
sae:J2012