Shorted or internally damaged auxiliary transmission fluid pump motor; Chafed, pinched, or shorted wiring between the pump and the control module; Corroded or loose electrical connectors at the pump or module; Failed transmission control module driver circuit for the pump; Fluid contamination or debris causing the pump to bind and draw excessive current; A seized pump rotor or bearing due to wear or lack of lubrication

DTC codes / P0Bxx · Hybrid propulsion / P0B05

P0B05Electric/Auxiliary Transmission Fluid Pump Motor Phase V Current High

P0B05 indicates that the transmission control module has detected an abnormally high current draw on the V phase of the electric auxiliary transmission fluid pump motor circuit. This pump maintains fluid pressure for shifts and cooling when the engine is not running or during auto start-stop events, and excessive current usually points to a shorted motor winding, damaged wiring, or a failing pump assembly.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyProfessional

AreaHybrid propulsion

Symptoms you may notice

Illumination of the check engine light or service transmission warning, often with no other noticeable symptoms
Harsh or delayed gear engagements, especially after an auto start-stop event
Transmission slipping or inability to shift into gear when the engine is off
Overheating of the transmission fluid or reduced cooling performance
A blown fuse or melted wiring near the auxiliary pump
The vehicle may enter limp mode or refuse to restart after stopping

Common causes, most likely first

Shorted or internally damaged auxiliary transmission fluid pump motor
Chafed, pinched, or shorted wiring between the pump and the control module
Corroded or loose electrical connectors at the pump or module
Failed transmission control module driver circuit for the pump
Fluid contamination or debris causing the pump to bind and draw excessive current
A seized pump rotor or bearing due to wear or lack of lubrication

How to diagnose and fix it

Scan all modules for stored and pending codes, and record freeze-frame data to confirm when the high current occurs
Visually inspect the pump wiring harness and connectors for chafing, corrosion, or loose pins
Measure the resistance of the pump motor windings and compare to specifications to check for a short
Use a current clamp or multimeter to measure actual current draw on the V phase circuit during pump activation
Check the pump fuse and relay, and test the control module output with a bidirectional scan tool if available
If wiring and connectors are good, replace the auxiliary transmission fluid pump assembly and clear codes
After repair, verify the pump operates correctly during auto start-stop and test-drive to confirm no return of the code

Before you replace the auxiliary pump

A chafed harness near the transmission mount or a corroded connector often mimics a failed pump, so always inspect wiring before condemning the motor.
The pump may only run during auto start-stop events, so the code can set without any drivability symptoms and may not reappear on a short test drive.
Low or contaminated transmission fluid can cause the pump to bind and draw high current, so check fluid condition and level before replacing parts.
A failing transmission control module driver can command the pump incorrectly, and replacing the pump alone will not fix the code if the module is at fault.
Some vehicles store this code after a low-voltage event or a jump start, so clear the code and verify it returns before starting diagnosis.

Can I keep driving with P0B05?

You can usually drive the vehicle short distances to a repair shop, but avoid relying on auto start-stop and do not tow heavy loads or drive at high speeds until the fault is fixed. If the transmission overheats or shifts harshly, stop driving and have the vehicle towed.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.