What Does P0B00 Mean?
The powertrain control module has detected a general electrical fault in the Phase U motor winding circuit of the auxiliary transmission fluid pump motor. This electric pump maintains transmission fluid pressure and flow when the engine is off (during EV mode or auto-stop). A fault in this circuit can result in inadequate transmission lubrication and cooling, potentially causing harsh shifts or transmission damage.
Common Causes
35%
Faulty auxiliary transmission fluid pump motor with degraded Phase U winding
25%
Damaged or corroded wiring harness in the Phase U motor circuit
20%
Corroded or loose connector pins at the pump motor or control module
15%
Auxiliary pump motor control module driver circuit failure
5%
Short to ground or power in the Phase U wiring
Diagnostic Steps
1
Read freeze frame data and note vehicle operating conditions (engine running/stopped, EV mode, transmission temperature) when the fault occurred.
2
Disconnect the auxiliary pump motor connector and measure Phase U winding resistance between the Phase U terminal and the common/neutral point. Compare with Phases V and W — all three should be within 10% of each other (typically 0.5-5 ohms depending on design).
3
Check for continuity between each Phase U wire and chassis ground to rule out a short-to-ground condition. Resistance should be greater than 10K ohms.
4
Inspect the motor connector and control module connector for signs of overheating, corrosion, water intrusion, or damaged pins. Clean and verify pin tension.
5
If winding resistance and wiring check normal, monitor the pump motor control module commands and Phase U current draw using the scan tool's bi-directional controls to command pump operation.
Estimated Repair Cost
$300 - $1,800
Parts + labor, varies by vehicle and location
The powertrain control module has detected a general electrical fault in the Phase U motor winding circuit of the auxiliary transmission fluid pump motor. This electric pump maintains transmission fluid pressure and flow when the engine is off (during EV mode or auto-stop). A fault in this circuit c...
The most common cause of P0B00 (Auxiliary Transmission Fluid Pump Motor Phase U Current) is: Faulty auxiliary transmission fluid pump motor with degraded Phase U winding
Typical repair costs for P0B00 range from $300 to $1,800, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Without the auxiliary pump, the transmission may not receive adequate fluid pressure during engine-off conditions (EV mode or idle stop). This can cause delayed engagement, harsh shifting, or accelerated wear. The vehicle will typically disable auto-stop and EV mode as a protective measure. Continued driving in engine-on mode is generally safe short-term, but repair should be prioritized.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0B00 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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