Powertrain, generic · Hybrid propulsion

P0C22 Electric/Auxiliary Transmission Fluid Pump Phase U-V-W Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P0C22 reports a high condition on the U-V-W phase circuits of the auxiliary pump motor, for example a phase lead shorted to the supply or a phase voltage that stays high while the inverter should pull it down. No manufacturer documents this exact code publicly. In GM's Volt tables the closest monitors are P0C28, which trips above 35 A on any phase within a few milliseconds to protect the IGBTs, and its own phase sensor codes P1E2B, P1E2E and P1E31 for readings above 30 A. The Hitachi sub-oil pump patent shows that phase currents are often calculated from a shared bus shunt, so a sensing error must be ruled out before the wiring is condemned. The pump stops and auto-stop is blocked. P0C21 is the low side, P0B02, P0B05 and P0B08 the per-phase high codes.

Likely causes

Phase lead shorted to supply voltage or to another phase
High-side switch of the pump inverter stuck conducting
Phase current sensing in the inverter reads too high
Shorted turns in the pump motor winding

Symptoms

  • MIL and hybrid or transmission warning
  • Pump shuts down, harsh engagement after stops

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–2,500
Time1–6 h

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

Parts involved

aux trans pump phase uvwaux trans pump inverter

Related codes

P0C20P0C21P0C28P0B02P0B05P0B08

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