What Does P0C20 Mean?
DTC P0C20 indicates an open circuit condition in the three-phase (U, V, W) motor winding circuit of the auxiliary transmission fluid pump. This electric pump uses a brushless DC motor driven by its own inverter/controller, and an open in any of the phase connections will prevent the pump from operating. Loss of this pump means the transmission loses auxiliary hydraulic pressure and lubrication flow, particularly critical during EV-only operation when the engine-driven pump is inactive.
Safety Warning
A non-functional auxiliary pump means no transmission fluid pressure during EV driving, which can cause gear disengagement, harsh shifting, or complete loss of drive. Transmission damage from inadequate lubrication is also possible if the condition persists.
Common Causes
30%
Disconnected or damaged connector at the auxiliary pump motor
25%
Broken wire in the pump phase wiring harness
20%
Open winding in one phase of the pump motor stator
15%
Corroded connector pins causing open circuit
10%
Failed pump controller output stage (open MOSFET)
Diagnostic Steps
1
Step 1: Check for companion DTCs P0C21 (low) and P0C22 (high) and the pump over-temperature codes (P0C1B–P0C1E). An open circuit code alone typically points to a wiring or connection issue.
2
Step 2: Inspect the electrical connector at the auxiliary transmission fluid pump for proper seating, corrosion, bent or backed-out pins, and water intrusion.
3
Step 3: Measure continuity on each of the three phase wires from the pump controller connector to the pump motor connector. An open reading on any phase confirms a wiring break.
4
Step 4: If wiring is intact, measure the pump motor winding resistance across all three phase pairs (U-V, V-W, U-W) at the pump connector. An open reading on any pair indicates a failed motor winding.
5
Step 5: If the motor windings and wiring are good, the pump controller output stage may have a failed MOSFET. Replace the pump controller module.
Estimated Repair Cost
$400 - $2,500
Parts + labor, varies by vehicle and location
DTC P0C20 indicates an open circuit condition in the three-phase (U, V, W) motor winding circuit of the auxiliary transmission fluid pump. This electric pump uses a brushless DC motor driven by its own inverter/controller, and an open in any of the phase connections will prevent the pump from operat...
The most common cause of P0C20 (Auxiliary Transmission Fluid Pump Phase U-V-W Circuit/Open) is: Disconnected or damaged connector at the auxiliary pump motor
Typical repair costs for P0C20 range from $400 to $2,500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
A non-functional auxiliary pump means no transmission fluid pressure during EV driving, which can cause gear disengagement, harsh shifting, or complete loss of drive. Transmission damage from inadequate lubrication is also possible if the condition persists.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0C20 to identify the root cause.
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Quick Info
Category
Powertrain
System
Hybrid/EV Transmission Auxiliary Pump
Difficulty
Type
Generic (SAE)
Recommended Tools
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