Faulty auxiliary transmission fluid pump motor with internal short or seized rotor; Short to ground in the pump motor power or ground wiring; Corroded, loose, or damaged electrical connector at the pump motor; Failed pump motor control module or relay that supplies power; Contaminated transmission fluid causing pump binding and increased current draw; PCM software calibration issue falsely reporting high current (rare)

DTC codes / P0Cxx · Hybrid propulsion / P0C28

P0C28Electric/Auxiliary Transmission Fluid Pump A Motor Current High

P0C28 indicates that the powertrain control module (PCM) has detected excessive current draw in the electrical circuit for the auxiliary transmission fluid pump motor, specifically the 'A' circuit. The PCM monitors the pump motor's current and flags this code when the measured current exceeds the calibrated threshold, which typically points to a short to ground, a failing pump motor, or a wiring fault.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyProfessional

AreaHybrid propulsion

Symptoms you may notice

Illumination of the malfunction indicator lamp (MIL) on the dashboard
Transmission may enter limp mode or fail to engage drive/reverse smoothly
Harsh or delayed shifting due to insufficient transmission fluid pressure
Overheating of the transmission fluid in hybrid or start-stop vehicles that rely on the auxiliary pump
Often no symptoms besides the warning light, especially if the pump is only intermittently overcurrent

Common causes, most likely first

Faulty auxiliary transmission fluid pump motor with internal short or seized rotor
Short to ground in the pump motor power or ground wiring
Corroded, loose, or damaged electrical connector at the pump motor
Failed pump motor control module or relay that supplies power
Contaminated transmission fluid causing pump binding and increased current draw
PCM software calibration issue falsely reporting high current (rare)

How to diagnose and fix it

Use a scan tool to verify P0C28 is current and check for related codes in the transmission control module (TCM).
Inspect the auxiliary pump motor connector and wiring for corrosion, chafing, or loose pins; repair as needed.
Measure resistance across the pump motor terminals and compare to manufacturer specification; replace motor if out of range.
Check the pump motor power and ground circuits for a short to ground using a multimeter and wiring diagram.
Test the pump motor control module or relay for proper operation and replace if faulty.
Perform a transmission fluid service if the fluid is contaminated or degraded, then clear codes and retest.
If all electrical checks pass, reprogram the PCM/TCM with the latest calibration and re-evaluate.

What the pump current code hides

A shorted pump motor winding can sometimes test normal with a basic ohmmeter when cold, so a load test or current ramp test is more reliable.
The auxiliary pump often runs only during auto-stop events or low-speed electric driving, so the fault may not appear during a short test drive.
Corrosion inside the pump connector can create resistance that mimics a failing motor, so always back-probe under load before condemning the pump.
This code can be set by a weak battery or charging system issue that causes voltage spikes, so check system voltage first.
Replacing the pump without checking the control module risk repeated failure if the module is intermittently shorting the circuit.

Can I keep driving with P0C28?

If the vehicle drives normally and the only symptom is the warning light, you may drive cautiously to a repair shop, but avoid heavy loads or long trips. If the transmission slips, overheats, or enters limp mode, stop driving and have the vehicle towed to prevent further damage.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.