Auxiliary Transmission Fluid Pump Motor Phase W Current Low
The P0B07 code indicates that the Powertrain Control Module (PCM) has detected a low current condition in phase W 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. Low current suggests an electrical fault such as high resistance, an open circuit, or a failing motor, which can lead to inadequate fluid circulation and potential transmission damage.
1. Symptoms You Will Notice
- Check Engine Light illuminated
- Transmission overheating
- Reduced fuel economy due to increased load on engine
- Possible transmission slipping or harsh shifting
2. Most Common Causes
- Faulty stator winding in the auxiliary pump motor phase W
- Loose connection or corrosion at the phase W wiring terminals
- Phase W wiring shorted to ground or open circuit
- Faulty auxiliary pump inverter/power module
- Defective TCM providing incorrect inverter control
- Excessive resistance in the phase W circuit due to damaged wiring or splices
3. Step-by-Step Diagnosis
Step 1: Scan for additional codes and record freeze frame data.
Step 2: Visually inspect the auxiliary pump connector and wiring for damage, corrosion, or loose pins.
Step 3: Using a multimeter, measure resistance between phase W and the other phases (U, V) at the pump connector; compare to specifications (typically 0.5-2 ohms).
Step 4: Check for voltage supply and ground at the pump connector with the engine running and transmission in gear.
Step 5: If wiring and connections are good, replace the auxiliary transmission fluid pump.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as low pump current can cause transmission overheating and damage. Have it diagnosed promptly.
How much does it cost to fix?▼
Diagnosis typically costs $50-$150. Replacing the auxiliary pump can range from $200-$600 including parts and labor.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.