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U063B Lost Communication With Coolant Bypass Valve Actuator A

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

Rotary coolant valves are often moved by a smart actuator that takes its target angle over LIN and reports back. U063B covers the case where actuator A no longer replies. Mercedes-Benz uses it in the drivetrain controller N127 (PTCU, CPC3) for the control valve of the high-temperature circuit; bulletin LI20.00-P-076708 for the GLC 254 and the facelifted GLE 167 (model year 2024) lists U063B00 and U063B87 (message missing) together with codes for fan 1, coolant pumps and an exhaust flap on the same LIN line. The check engine lamp comes on, a coolant service message appears and the radiator fan runs flat out. For the GLC with PTCU version 22A the cure is new software; otherwise connectors and LIN wiring are inspected. Electrical faults of the valve drive itself are P0E75 to P0E7A.

Likely causes

Outdated drivetrain controller software (Mercedes PTCU version 22A)
Damaged, chafed or corroded LIN wiring or intermediate connectors
Electronics in valve actuator A failed
Missing supply voltage or ground at the actuator

Symptoms

  • Check engine light with coolant service message
  • Radiator fan permanently running at full speed and noisy
  • Further LIN codes (fan, coolant pumps, exhaust flap) stored together

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–900
Time0.3–2.5 h

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

Parts involved

coolant bypass valve actuator avehicle bus wiring

Related codes

U063CP0E75P0E76P0E77P0E78P0E79P0E7AU0615U0632U0698

References: static.nhtsa.gov, static.nhtsa.gov, hella.com.