What it means
The vehicle bus reports loss of communication with smart reductant (DEF/AdBlue) level sensor C. Tank-level monitoring switches to a substitute model; refill warnings may be incorrect.
At a glance
- Usually lights the warning light of the system that lost communication
- Affects emissions; the car can fail an emissions test
How it works
The smart reductant level sensor C reports DEF/AdBlue tank information over the vehicle network. The receiving module sets U061B when expected messages from this specific sensor stop arriving, so it may estimate tank level instead and give unreliable refill warnings.
Common causes
Most likely first.
- Bus wiring open or shorted
- Module without power or ground
- Module failed
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
How to diagnose it
- Scan all modules for communication codes and record freeze-frame data to see whether other network faults appeared at the same time.
- Check live data for reductant level sensor C and compare its reported status with the tank-level display and the other available sensor data.
- Inspect sensor C's connector and nearby bus wiring for corrosion, loose pins, damage, or a short or open circuit.
- Check the sensor module's power and ground under the conditions specified by the manufacturer.
- Test the relevant network circuit for continuity and shorts using the manufacturer's wiring information.
- If wiring, power, and ground are sound, confirm that sensor C is transmitting before considering module replacement.
Common fixes
- Repair damaged or corroded wiring or connector terminals at reductant level sensor C.
- Restore the sensor module's power or ground connection.
- Repair an open or short in the vehicle network wiring.
- Replace the failed sensor module if its supply and network circuit test correctly.
Can I keep driving?
You can usually drive cautiously if the vehicle runs normally, but do not rely on the DEF/AdBlue level warning to tell you when to refill. Address the fault promptly because an inaccurate level estimate can lead to a missed refill warning or an emissions-related restriction.
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.