What Does P0B07 Mean?
The auxiliary transmission fluid pump motor controller has detected that Phase W winding current is below the minimum acceptable threshold during pump operation. With one of the three motor phases conducting insufficient current, the pump will produce reduced and uneven torque, leading to inadequate fluid flow rate. The pump may stall under load, leaving the transmission without supplemental fluid pressure during engine-off conditions.
Common Causes
35%
High-resistance connection in the Phase W circuit (corroded or loose pin)
25%
Developing open circuit in the Phase W motor winding
20%
Weakened Phase W driver MOSFET in the control module
15%
Partially broken Phase W conductor with reduced effective cross-section
5%
Low supply voltage to the controller reducing overall drive capability
Diagnostic Steps
1
Monitor all three phase currents in real-time while the pump is running. Confirm Phase W is significantly lower than Phase U and Phase V.
2
Disconnect the motor and measure Phase W resistance compared to the other two phases. Higher resistance in Phase W points to a winding problem.
3
Perform a voltage drop test on the Phase W circuit end-to-end while the pump is being commanded on. Excessive voltage drop (above 0.5V) indicates a high-resistance point in the wiring or connector.
4
Inspect Phase W pins at the motor connector and controller connector for oxidation, reduced spring tension, or heat discoloration. Apply contact cleaner and re-seat.
5
If all external circuits test normal, isolate the controller by swapping Phase W and Phase U connections at the controller output — if the low current follows the controller pin, the module driver is at fault.
Estimated Repair Cost
$250 - $1,600
Parts + labor, varies by vehicle and location
The auxiliary transmission fluid pump motor controller has detected that Phase W winding current is below the minimum acceptable threshold during pump operation. With one of the three motor phases conducting insufficient current, the pump will produce reduced and uneven torque, leading to inadequate...
The most common cause of P0B07 (Auxiliary Transmission Fluid Pump Motor Phase W Current Low) is: High-resistance connection in the Phase W circuit (corroded or loose pin)
Typical repair costs for P0B07 range from $250 to $1,600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Reduced Phase W current means the auxiliary pump may not deliver adequate fluid pressure during engine-off operation. Auto-stop and EV mode will be disabled as a precaution. Continued driving with the engine running is safe, but repair is needed to restore full hybrid capability.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0B07 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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