P20AC
Reductant Metering Unit Temperature Sensor Circuit
A general electrical fault is reported on the temperature sensor inside the DEF metering unit — used to protect the unit from over-temperature and to compensate for fluid viscosity.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: hard
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)
Common causes
Ordered by how often each turns out to be the cause.
- Sensor element failedCommon
- Harness faultPossible
Parts involved
- Reductant Metering Unit
- Reductant Metering Temp Sensor
P20AC is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.