What it means
The ECM detects a generic fault on the reductant temperature B sensor circuit. Reading cannot be used reliably for control.
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 emissions reductant, such as AdBlue or DEF, in the aftertreatment system. The engine control module monitors its circuit for a usable signal; this code sets when it detects a fault that prevents reliable temperature reporting.
Common causes
Most likely first.
- Sensor failed
- 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, NOx, or aftertreatment codes before clearing anything.
- Read sensor B's live temperature and compare it with other available reductant temperature readings and ambient conditions for plausibility.
- Inspect the sensor B connector and exposed harness for corrosion, fluid ingress, loose pins, or damage.
- Check the sensor B signal, supply, and ground circuits for continuity, shorts, and poor connections using the vehicle wiring information.
- Test sensor B and its circuit against the manufacturer's specification, then verify that the reading is usable after repair.
Common fixes
- Clean and secure corroded or loose sensor B connector terminals.
- Repair damaged wiring or poor connections in the reductant temperature sensor B circuit.
- Replace reductant temperature sensor B if it fails the specified circuit test.
Can I keep driving?
Driving may be possible initially, but treat any NOx warning or AdBlue/DEF countdown seriously: the vehicle may eventually restrict operation or prevent restarting. Avoid delaying diagnosis, and do not rely on continued driving once a countdown is displayed.
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.