Network, generic

U061B Lost Communication With Reductant Level Sensor C

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modeNo

Level sensor C is a third level input of a reductant system and exists only on layouts with more than one tank or measuring point. No manufacturer publicly documents U061B or explains which part carries the letter C. The code says that this third sensor's digital messages have stopped or keep arriving corrupted, so its reading is treated as unknown. Because CARB counts the reductant supply among the SCR functions an OBD system must watch, and asks for a separate code whenever a digital input stops communicating, the fault is emission-related even if levels A and B still report. Volvo's guide for its CAN-connected truck tank sensor starts with the harness and the pins, looking for damage, corrosion and water, which is also the sensible first step here. P21AD to P21B1 cover the circuit faults of sensor C.

Likely causes

Damaged pins, corrosion or water in the connector of sensor C

Harness to the additional tank or measuring point damaged

Internal failure of level sensor C

Symptoms

Malfunction indicator lamp
Implausible DEF quantity on the display

Repair estimate

DifficultyMediumWorkshop job

Parts and labour€80–1,200

Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

reductant level sensor csensor wiring

References: law.cornell.edu, static.nhtsa.gov.