What Does P0B03 Mean?
The powertrain control module has detected a general electrical fault in the Phase V motor winding circuit of the auxiliary transmission fluid pump. This three-phase electric pump is critical for maintaining transmission fluid flow during hybrid engine-off modes. A Phase V circuit fault will prevent proper three-phase motor operation, causing the pump to run poorly, vibrate excessively, or fail to operate entirely.
Common Causes
35%
Faulty auxiliary transmission fluid pump motor with degraded Phase V winding
25%
Damaged wiring or corroded connector in the Phase V motor circuit
20%
Loose or corroded connector pins at the pump motor or its controller
15%
Pump motor control module Phase V driver circuit failure
5%
Short to ground or to battery voltage in the Phase V wiring
Diagnostic Steps
1
Read freeze frame data and note the vehicle operating mode and transmission temperature when the fault set. Determine whether the pump was being commanded on at the time.
2
Disconnect the pump motor connector and measure Phase V winding resistance between the Phase V terminal and common/neutral. Compare with Phases U and W — all three should be within 10% of specification.
3
Test for short-to-ground by measuring insulation resistance from each Phase V wire to chassis ground. Resistance must exceed 10K ohms.
4
Inspect both the motor-side and controller-side connectors for corrosion, damaged pins, water ingress, or heat discoloration. Verify proper pin seating and tension.
5
Command the auxiliary pump on via scan tool and monitor Phase V current compared to Phase U and Phase W. An absent or erratic Phase V current confirms the circuit fault location.
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 V motor winding circuit of the auxiliary transmission fluid pump. This three-phase electric pump is critical for maintaining transmission fluid flow during hybrid engine-off modes. A Phase V circuit fault will prevent...
The most common cause of P0B03 (Auxiliary Transmission Fluid Pump Motor Phase V Current) is: Faulty auxiliary transmission fluid pump motor with degraded Phase V winding
Typical repair costs for P0B03 range from $300 to $1,800, depending on the vehicle, location, and whether you do it yourself or go to a shop.
The transmission auxiliary pump ensures fluid flow during engine-off conditions. Without it, auto-stop and EV mode will be disabled. Continued driving with the engine running poses no immediate safety risk, but the fault should be repaired to restore hybrid functionality and 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 P0B03 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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