Powertrain, generic · Hybrid propulsion

P0C1B Electric/Auxiliary Transmission Fluid Pump Control Module Internal Temperature Too High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P0C1B is a protection code: the electronics that drive the auxiliary transmission fluid pump measure a valid but excessive internal temperature. No manufacturer documents this exact code publicly. GM shows the same function on the 2016 Cadillac ELR pump controller under its own code P1E37, an in-range overtemperature above 98 °C that could damage the inverter, checked only when the sensor itself is plausible. A Honda patent for a CVT pump explains the reaction: once the board temperature passes a limit, the control unit opens the pump relay and keeps the pump off until the fluid has cooled. The pump then stops, so start-stop and pressure support are lost. P0C1C to P0C1F cover faults of the temperature sensor itself and must be excluded first.

Likely causes

High transmission fluid temperature from heavy load, towing or a weak fluid cooler
Pump running against high resistance (binding, clogged filter) and heating its driver
Poor heat transfer from the module (mounting, contamination) or internal module fault

Symptoms

  • Engine auto-stop temporarily unavailable
  • Transmission or hybrid warning, MIL depending on manufacturer
  • Harsh engagement when driving off after a stop

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–1,800
Time0.5–4 h

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

Parts involved

aux trans pump control module

Related codes

P0C1CP0C1DP0C1EP0C1FP0B0DP2797

References: law.cornell.edu, gsi.ext.gm.com, patents.google.com.