What it means
The reductant level sensor B circuit reading is outside the expected range or does not perform as expected. The code does not establish that a float is used or identify the cause.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Reductant level sensor B reports a level-related signal from the DEF or AdBlue system to the control module. This code sets when that signal is outside the expected range or does not change as expected; it does not establish that the sensor uses a float or identify the failed part.
Common causes
Most likely first.
- Float arm sticks
- Sensor element aged beyond calibration window
- Sensor mounting loose - signal damping
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
- Record freeze-frame data and compare live sensor B readings with the actual DEF level and any related reductant codes.
- Check whether the reported level changes appropriately after a known change in DEF quantity, following the vehicle's approved procedure.
- Inspect sensor B's mounting, connector, and harness for looseness, contamination, corrosion, or damage that could affect the reading.
- Check the sensor B signal and its power and ground against the wiring diagram and manufacturer's specification.
- If the circuit checks out, test the sensor and its mounting for a sticking or unstable reading before replacing parts.
Common fixes
- Secure a loose sensor B mounting or connector.
- Repair corroded terminals or damaged wiring affecting the sensor B signal.
- Correct a sensor installation or contamination issue that prevents a stable reading.
- Replace reductant level sensor B if testing confirms its output is outside specification.
Can I keep driving?
You can usually drive briefly if the vehicle operates normally, but confirm the DEF level and arrange diagnosis soon. An inaccurate reading can leave the system unable to track reductant level and may lead to emissions warnings or a no-start countdown on some vehicles.
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.