Network, generic

U061A Lost Communication With Reductant Level Sensor B

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modeNo

Some SCR tanks carry more than one level measurement, for example a second sensing element, a second tank chamber or a separate sender; which point counts as B is the manufacturer's choice, and no public document assigns it. U061A is stored when the controller stops receiving usable digital frames from level sensor B while sensor A may still report normally. That pattern points to the wiring branch, connector or electronics of the second sensor rather than to the network as a whole. Supplier sensors such as SSI's ultrasonic DEF unit put level and temperature on a J1939 CAN link, so a dead sensor looks to the controller like any missing node. Circuit-type faults of the same sensor are P21A8 to P21AC. Expect a warning lamp and a DEF reading that no longer matches the tank.

Likely causes

Open or chafed wire in the branch that feeds only level sensor B

Water or corrosion in the connector of sensor B

Level sensor B electronics failed

Symptoms

Check engine light or DEF system warning
DEF level shown wrongly or not at all

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 bsensor wiring

References: ssi-sensors.com, law.cornell.edu.