What it means
The control module has detected a fault in the reductant level sensor B circuit. The code does not specify the circuit failure or sensor arrangement.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The reductant system stores and supplies DEF or AdBlue for exhaust aftertreatment, and sensor B reports a level-related signal to the control module. This code sets when the module detects an electrical fault in sensor B's circuit; the code alone does not identify whether the problem is the sensor, wiring, connector, power, or ground.
Common causes
Most likely first.
- Failed level sensor B
- Open or shorted sensor wiring
- Loose or corroded connector
- Poor sensor ground or power supply
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 check live readings for reductant level sensor B alongside any other reductant or aftertreatment codes.
- Verify the actual DEF level using the vehicle's display or approved checking method, since a circuit fault can make the reported level unreliable.
- Inspect sensor B's connector and accessible harness for corrosion, moisture, loose terminals, or damaged insulation.
- With the correct wiring information, check sensor B's power and ground and test its signal circuit for opens or shorts.
- If wiring and supplies meet the manufacturer's specification, test sensor B and replace it only if it fails.
Common fixes
- Reconnect and secure a loose sensor B connector.
- Clean or repair corroded terminals and damaged sensor B wiring.
- Repair a failed power or ground connection to sensor B.
- Replace reductant level sensor B if circuit testing confirms it is faulty.
Can I keep driving?
You can usually drive briefly if the vehicle operates normally, but check and maintain the DEF level and arrange diagnosis promptly. A persistent fault can trigger 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.