Auxiliary Transmission Fluid Pump Motor Phase V Current Low
The P0B04 code indicates that the powertrain control module (PCM) has detected a low current condition in phase V 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. A low current reading suggests increased resistance or an open circuit in the motor windings, wiring, or connector for phase V, which can lead to reduced pump performance and potential transmission damage.
1. Symptoms You Will Notice
- Check Engine Light illuminated
- Transmission overheating or slipping
- Reduced fuel economy due to increased transmission drag
- Possible transmission shudder or harsh shifting
2. Most Common Causes
- Faulty auxiliary transmission fluid pump motor (open or shorted winding in phase V)
- Poor connection or corrosion at the phase V wiring connectors
- High resistance in the wiring to the auxiliary pump motor
- Failed inverter or control module for the auxiliary pump motor
- Defective TCM with incorrect phase V control
3. Step-by-Step Diagnosis
Step 1: Use a scan tool to retrieve all codes and freeze frame data.
Step 2: Visually inspect the auxiliary pump connector and wiring for damage, corrosion, or loose pins.
Step 3: Measure resistance between phase V terminal and motor ground; compare to specifications (typically 0.5-2 ohms).
Step 4: Check for continuity and shorts in the wiring from PCM to pump.
Step 5: If wiring is okay, replace the auxiliary transmission fluid pump motor.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended. Low pump current can lead to inadequate transmission cooling and lubrication, potentially causing severe internal damage. Have the vehicle inspected and repaired promptly.
How much does it cost to fix?▼
Diagnosis typically costs $50-$150. Replacing the auxiliary pump motor can range from $200-$600 including parts and labor, depending on vehicle make and model.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.