What Does P0B04 Mean?
The auxiliary transmission fluid pump motor control module has detected that Phase V motor current is below the expected minimum during pump operation. Insufficient current in one phase of a three-phase motor causes imbalanced operation, reduced torque output, increased vibration, and potential motor stalling. The auxiliary pump may not maintain adequate transmission fluid pressure.
Common Causes
35%
High-resistance connection in the Phase V circuit at a connector or splice
25%
Developing open circuit in the Phase V motor winding
20%
Phase V driver MOSFET in the control module degraded or partially failed
15%
Chafed or partially broken Phase V wire with reduced conductor cross-section
5%
Insufficient supply voltage to the control module reducing drive capability
Diagnostic Steps
1
Monitor Phase V current in real-time with the scan tool while the pump is running. Compare to Phase U and Phase W — Phase V should be within 10% of the other phases.
2
Disconnect the pump motor and measure Phase V winding resistance compared to Phase U and Phase W. An elevated Phase V resistance indicates winding degradation.
3
Perform voltage drop testing across the Phase V circuit while the pump is energized. Check from the control module output pin to the motor terminal — excessive drop indicates a high-resistance connection.
4
Inspect Phase V connector pins on both ends for oxidation, carbon buildup, or reduced contact tension. Clean contacts and apply dielectric grease after verification.
5
If the motor and wiring test normal, the control module Phase V driver may be degraded. Verify by swapping Phase V and Phase U connections at the controller and checking if the low-current condition moves to the swapped phase.
Estimated Repair Cost
$250 - $1,600
Parts + labor, varies by vehicle and location
The auxiliary transmission fluid pump motor control module has detected that Phase V motor current is below the expected minimum during pump operation. Insufficient current in one phase of a three-phase motor causes imbalanced operation, reduced torque output, increased vibration, and potential moto...
The most common cause of P0B04 (Auxiliary Transmission Fluid Pump Motor Phase V Current Low) is: High-resistance connection in the Phase V circuit at a connector or splice
Typical repair costs for P0B04 range from $250 to $1,600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Low Phase V current reduces auxiliary pump effectiveness during engine-off operation. The vehicle will likely disable auto-stop and EV mode. Engine-on driving remains safe, but repair should be completed to restore full hybrid functionality and ensure adequate transmission lubrication.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0B04 to identify the root cause.
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Quick Info
Category
Powertrain
System
Hybrid Transmission Auxiliary Systems
Difficulty
Type
Generic (SAE)
Recommended Tools
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