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U0647 Lost Communication With Motor Electronics Coolant Pump B

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modePossible

Cars fitted with two or more drive units, or with separate loops for the motor and its inverter, may fit a second networked pump in the motor electronics circuit, called B. U0647 is logged when this pump no longer returns its status frames. Public manufacturer documentation for U0647 does not exist. Since it is a separate node, the typical clue is that pump A and the rest of the bus still communicate, which narrows the search to pump B's own branch of wiring, its connector and its fuse. The conventional circuit codes for this pump are P0B38 to P0B3A, with P0C74 for performance and P2D05 to P2D09 for internal pump faults. Electric pumps such as Bosch's PCE generation take LIN commands and diagnose themselves. Expect reduced power from the axle that pump B cools.

Likely causes

Wiring branch or fuse that serves only pump B open

Pump B connector corroded or not fully seated

Pump B electronics failed

Symptoms

Hybrid or EV warning lamp, MIL on hybrids
Power limited on one drive unit

Repair estimate

DifficultyMediumWorkshop job

Parts and labour€60–700

Time0.5–2.5 h

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

Parts involved

motor electronics coolant pump bvehicle bus wiring

References: law.cornell.edu, bosch-mobility.com.