What it means
The reductant temperature B signal does not match plausibility checks against related signals. Sensor drift.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
- The engine or gearbox may go into limp mode
How it works
Reductant temperature sensor B measures the temperature of the aftertreatment system's reductant, such as AdBlue or DEF. The control module compares this reading with related signals and conditions; this code sets when sensor B's reading does not behave plausibly, even if the circuit is not clearly open or shorted.
Common causes
Most likely first.
- Sensor fault
- Wiring or connector fault
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)
How to diagnose it
- Save freeze-frame data and check for related reductant or NOx codes that could affect the temperature plausibility check.
- Compare sensor B's live temperature with ambient conditions and other available reductant temperature readings, both cold and as the system warms.
- Inspect sensor B's connector and harness for corrosion, loose terminals, fluid ingress, or heat damage.
- Check the signal, supply, and ground connections for resistance or intermittent contact that could offset the reading.
- Test sensor B's response against the manufacturer's specification across the relevant temperature range.
Common fixes
- Clean and secure the sensor B connector if its terminals are dirty or loose.
- Repair wiring or connections that cause an offset or unreliable sensor B reading.
- Replace reductant temperature sensor B if it drifts outside the manufacturer's specification.
Can I keep driving?
Driving may be possible at first, but an active NOx warning or AdBlue/DEF countdown can lead to restricted operation or a no-start condition. Arrange diagnosis promptly and follow any displayed countdown warnings.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.