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U0624 Lost Communication With Coolant Pump B

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

Some engines carry a second electric coolant pump, for instance one that keeps coolant moving through the turbocharger after shutdown or feeds a separate heater or low-temperature loop. Which pump is B is decided by the manufacturer. No manufacturer documents U0624 publicly; GM uses U0623 and U062F for its LIN pumps instead. The code means that pump B no longer answers on its data link. Bosch's PAD2 and PCE 2.0 pumps illustrate the design: speed set by PWM or LIN and a built-in diagnostic function that reports faults to the controlling unit. CARB asks for an approved monitoring plan when an electric pump rather than a thermostat governs engine coolant temperature. Wiring and connectors come first; P261A to P261D cover the pump's control circuit.

Likely causes

Signal, supply or ground wire to pump B damaged
Fuse or relay feeding pump B open
Pump electronics failed, sometimes after overheating or a seized rotor

Symptoms

  • Warning lamp
  • Reduced heater output or higher component temperatures after shutdown

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–800
Time0.3–2.5 h

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

Parts involved

coolant pump bvehicle bus wiring

Related codes

P261AP261BP261CP261DU0623U062F

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