Auxiliary Transmission Fluid Pump Motor Current High
The P0C28 code indicates that the Powertrain Control Module (PCM) has detected an abnormally high current draw from the auxiliary transmission fluid pump motor. This pump is responsible for circulating transmission fluid to cool and lubricate the transmission, especially during stop-start events or when the engine is off. High current can be caused by a failing pump motor, electrical short, or mechanical binding. If left unaddressed, it may lead to transmission overheating, reduced lubrication, and potential transmission damage.
1. Symptoms You Will Notice
- Check Engine Light illuminated
- Transmission overheating or slipping
- Reduced fuel economy
- Transmission warning message on dashboard
2. Most Common Causes
- Short to ground in the auxiliary pump motor wiring
- Auxiliary pump motor with internal winding short circuit
- Poor connection or corroded terminal at the motor connector
- Faulty or internally stuck auxiliary pump control relay
- Damaged output driver in the transmission control module (TCM)
- Pump motor resistance below manufacturer specifications
3. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data.
Step 2: Inspect pump wiring and connector for damage, corrosion, or shorts.
Step 3: Measure pump motor resistance and compare to specifications; check for shorts to ground.
Step 4: Test pump operation by commanding it on with a scan tool; listen for unusual noises.
Step 5: If pump is seized or draws high current, replace the auxiliary pump assembly.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended. High current can damage the pump or wiring, and reduced fluid circulation may cause transmission overheating and failure.
How much does it cost to fix?▼
Repair costs typically range from $200 to $600, including parts and labor, depending on the vehicle and whether the pump or wiring needs replacement.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.