Auxiliary Transmission Fluid Pump Motor Phase U Current High
The P0B02 code indicates that the Powertrain Control Module (PCM) has detected an excessively high current draw on phase U of 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 motor, short circuit, or mechanical binding, leading to potential transmission overheating or damage.
1. Symptoms You Will Notice
- Check Engine Light illuminated
- Transmission overheating
- Reduced transmission performance or shifting issues
- Auxiliary pump not operating when expected
2. Most Common Causes
- Short circuit to ground in the U-phase winding of the auxiliary pump motor
- Short circuit between stator phases (U-V or U-W)
- Fault in the inverter/driver module supplying three-phase current to the motor
- Low internal resistance in the U-phase winding due to overheating or insulation breakdown
- Poor connection or corroded terminal in the U-phase wiring causing erroneous readings
- Fault in the inverter's internal current sensor or TCM monitoring the U-phase
3. Step-by-Step Diagnosis
Step 1: Scan for additional codes and record freeze frame data.
Step 2: Visually inspect pump motor wiring and connector for damage or corrosion.
Step 3: Measure resistance and current draw on phase U of the pump motor using a multimeter and compare to specifications.
Step 4: Test pump operation by commanding it on with a scan tool and monitor current draw.
Step 5: If wiring and motor test OK, check the pump control module and replace if faulty.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended. High current can damage the pump or control module, and reduced transmission cooling may lead to overheating and costly repairs.
How much does it cost to fix?▼
Repair costs typically range from $150 to $400, depending on whether the pump motor, wiring, or control module needs replacement. Labor and parts vary by vehicle.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.