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U063D Lost Communication With Hybrid/EV Electronics Coolant Pump A

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modePossible

The first electric pump of the power electronics loop, A, circulates coolant through the inverter, DC/DC converter and similar parts. Pumps of this class, such as Bosch's PAD2, take their speed command via PWM or LIN and run their own diagnosis; with LIN the controller also expects regular status replies. U063D is set when pump A stops answering. No manufacturer documents U063D publicly. California's OBD II regulation covers the outputs of inverter cooling too, which makes a lit MIL likely on hybrids. If the pump is dead rather than just mute, P2C68 (stalled) or P0CEA (performance) tend to follow. Pumps B and C report the same fault as U02BA and U02C1. The electronics heat up and the system cuts power.

Likely causes

Blown fuse or open supply/ground to electronics coolant pump A

LIN wire to the pump open, shorted or chafed

Pump electronics failed, often after running dry or overheating

Fault in the hybrid or thermal controller acting as bus master

Symptoms

Hybrid system warning and MIL
Reduced electric drive power or engine kept running on hybrids
Inverter or electronics overtemperature messages

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

hv electronics coolant pump avehicle bus wiring

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