What it means
The reductant level sensor B signal is stuck or not updating as expected. The code does not establish that the sensor uses a float 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 provides a separate DEF/AdBlue level signal to the emissions control system. This code sets when sensor B's signal fails to update as expected; it can leave the level estimate unreliable and does not establish the sensor's physical design or the cause.
Common causes
Most likely first.
- Reductant level sensor B failed
- Sensor wiring open or shorted
- Loose or corroded connector
- Reductant deposits interfering with sensor operation
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
- Read freeze-frame data and live reductant level readings, comparing sensor B with sensor A where available to determine whether B alone remains fixed.
- Check the actual DEF/AdBlue quantity using the vehicle's approved method and compare it with the dashboard indication before assuming the tank is empty or full.
- Inspect sensor B's connector and wiring for loose pins, corrosion, moisture, damage, or chafing.
- Check the sensor B signal and supply/ground circuits using the manufacturer's wiring diagram and specification, looking for an unchanging signal or an open/short.
- If wiring is sound, inspect the sensor assembly and tank area for deposits or obstruction, then test sensor B according to the manufacturer's procedure.
Common fixes
- Correct the actual DEF/AdBlue level if it is outside the normal operating range.
- Clean and secure corroded or loose sensor B connector terminals.
- Repair damaged or open/shorted sensor B wiring.
- Clean reductant deposits if they are interfering with the sensor, or replace sensor B if testing confirms failure.
Can I keep driving?
You can generally drive if the vehicle runs normally, but do not rely on the displayed DEF/AdBlue level because sensor B may be stuck. A persistent emissions warning can lead to a no-start countdown, so check the fluid level by the approved method and heed any countdown.
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.