What Does P0B01 Mean?
The auxiliary transmission fluid pump motor control module has detected that the Phase U motor winding current is below the expected minimum during pump operation. This low current condition indicates the Phase U circuit is not conducting adequately, which will cause the three-phase pump motor to run inefficiently, vibrate, or stall. Transmission fluid flow during EV or auto-stop mode will be compromised.
Common Causes
35%
High-resistance connection in the Phase U circuit (corroded connector or loose pin)
25%
Partially open Phase U motor winding (developing open circuit)
20%
Control module Phase U low-side driver weakening or partially failed
15%
Damaged or chafed Phase U wire increasing circuit resistance
5%
Low supply voltage to the pump motor control module
Diagnostic Steps
1
Monitor live data for Phase U current during pump operation and compare with Phase V and Phase W currents. A significantly lower Phase U reading confirms the circuit issue.
2
Disconnect the pump motor connector and measure Phase U winding resistance. Compare with Phase V and W — Phase U should not be more than 10% higher than the others. An elevated reading indicates a developing open in the winding.
3
Perform a voltage drop test on the Phase U circuit by measuring voltage at the motor connector while the pump is commanded on. Excessive voltage drop (above 0.5V) indicates a high-resistance connection in the wiring or connector.
4
Inspect the Phase U connector pins at both the motor and the control module for corrosion, pitting, or reduced spring tension. Clean with electrical contact cleaner and verify proper seating.
5
If wiring and motor test normal, swap the Phase U and Phase V connections at the control module to determine if the low-current condition follows the winding or the driver — this isolates whether the fault is in the motor or the module.
Estimated Repair Cost
$250 - $1,600
Parts + labor, varies by vehicle and location
The auxiliary transmission fluid pump motor control module has detected that the Phase U motor winding current is below the expected minimum during pump operation. This low current condition indicates the Phase U circuit is not conducting adequately, which will cause the three-phase pump motor to ru...
The most common cause of P0B01 (Auxiliary Transmission Fluid Pump Motor Phase U Current Low) is: High-resistance connection in the Phase U circuit (corroded connector or loose pin)
Typical repair costs for P0B01 range from $250 to $1,600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Reduced auxiliary pump performance can lead to insufficient transmission lubrication during engine-off operation. The vehicle will typically disable auto-stop and limit EV mode. Continued driving with the engine running is safe, but the pump issue should be repaired to prevent long-term transmission wear.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0B01 to identify the root cause.
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Quick Info
Category
Powertrain
System
Hybrid Transmission Auxiliary Systems
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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