What Does P0B08 Mean?
The auxiliary transmission fluid pump motor control module has detected that Phase W motor winding current exceeds the maximum safe operating limit. Excessive current in one phase of a three-phase motor typically indicates a shorted winding, ground fault in the wiring, or significant mechanical resistance in the pump. This overcurrent condition can rapidly damage the motor, control module, and associated wiring if not addressed.
Safety Warning
Overcurrent creates a risk of wiring overheating and potential fire. The controller will shut down the pump to prevent damage. If you smell burning insulation or see smoke near the transmission area, stop driving immediately and have the vehicle towed. Otherwise, the vehicle can be driven with the engine running, but repair urgently.
Common Causes
35%
Shorted turns in the Phase W motor winding
25%
Phase W wiring shorted to ground or to another phase
20%
Pump mechanical binding causing excessive motor load
15%
Shorted Phase W MOSFET in the control module
5%
Water or fluid contamination inside motor causing insulation breakdown
Diagnostic Steps
1
Compare all three phase currents in live data while the pump is operating. Phase W reading significantly higher than Phases U and V confirms the overcurrent condition.
2
Disconnect the motor and measure Phase W winding resistance. A value significantly lower than Phase U or Phase V indicates inter-turn shorts. Measure insulation resistance from Phase W to motor case — should exceed 1M ohm.
3
With the motor disconnected, measure Phase W wire insulation resistance to ground and to each other phase. Any reading below 10K ohms indicates a wiring fault that must be repaired.
4
Check for pump mechanical binding by attempting to rotate the motor shaft. A seized pump will draw excessive current on all phases. Partially binding conditions may stress individual phases differently.
5
Inspect the motor housing, connector seals, and wire entry points for fluid leaks, water intrusion, or heat damage. Transmission fluid leaking into the motor can cause winding insulation failure.
Estimated Repair Cost
$400 - $2,000
Parts + labor, varies by vehicle and location
The auxiliary transmission fluid pump motor control module has detected that Phase W motor winding current exceeds the maximum safe operating limit. Excessive current in one phase of a three-phase motor typically indicates a shorted winding, ground fault in the wiring, or significant mechanical resi...
The most common cause of P0B08 (Auxiliary Transmission Fluid Pump Motor Phase W Current High) is: Shorted turns in the Phase W motor winding
Typical repair costs for P0B08 range from $400 to $2,000, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Overcurrent creates a risk of wiring overheating and potential fire. The controller will shut down the pump to prevent damage. If you smell burning insulation or see smoke near the transmission area, stop driving immediately and have the vehicle towed. Otherwise, the vehicle can be driven with the engine running, but repair urgently.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0B08 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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