Damaged or chafed wiring in the pump motor phase V circuit, including open or shorted conductors; Corroded or loose electrical connector at the auxiliary pump motor or transmission control module; Failed auxiliary transmission fluid pump motor, such as a shorted or open phase winding; Faulty transmission control module driver circuit for the pump motor; Low or contaminated transmission fluid causing pump overload and abnormal current draw; Internal mechanical binding in the auxiliary pump assembly; Aftermarket electrical accessories improperly tapped into the pump circuit

DTC codes / P0Bxx · Hybrid propulsion / P0B03

P0B03Electric/Auxiliary Transmission Fluid Pump Motor Phase V Current

P0B03 indicates that the electric auxiliary transmission fluid pump motor's phase V current is outside the expected range, as detected by the transmission control module monitoring the pump's electrical draw. This pump maintains fluid pressure when the engine is off or during auto start-stop events, so a phase current fault can disable that function and trigger the warning light.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyProfessional

AreaHybrid propulsion

Symptoms you may notice

Illumination of the transmission or powertrain warning light, often with no other noticeable symptoms
Rough or delayed engagement when accelerating from a stop after an auto start-stop event
Harsh shifting or slipping during low-speed maneuvers when the engine is not running
The vehicle may enter limp mode or refuse to restart after shutting off at a traffic light
A whining or humming noise from the transmission area that changes with pump operation
Inconsistent transmission behavior that worsens in stop-and-go traffic

Common causes, most likely first

Damaged or chafed wiring in the pump motor phase V circuit, including open or shorted conductors
Corroded or loose electrical connector at the auxiliary pump motor or transmission control module
Failed auxiliary transmission fluid pump motor, such as a shorted or open phase winding
Faulty transmission control module driver circuit for the pump motor
Low or contaminated transmission fluid causing pump overload and abnormal current draw
Internal mechanical binding in the auxiliary pump assembly
Aftermarket electrical accessories improperly tapped into the pump circuit

How to diagnose and fix it

Verify battery voltage and charging system output, then clear the code and test-drive to confirm it returns
Inspect the auxiliary pump motor connector and harness for corrosion, chafing, or loose pins, and repair as needed
Measure resistance and voltage drop on the phase V circuit between the pump motor and control module, comparing to manufacturer specifications
Check transmission fluid level and condition, and service the fluid if it is low or contaminated
Perform an active pump test with a scan tool to command the auxiliary pump and observe current draw and pressure response
If electrical checks pass, remove the auxiliary pump motor and bench-test it or substitute a known-good unit to isolate the fault
If the pump motor tests good, diagnose the transmission control module driver circuit and replace the module only after confirming all external wiring is sound

What the phase V current code hides

A weak or aging battery can cause this code because the auxiliary pump draws high current during auto start-stop events, and low system voltage skews the current feedback the control module monitors.
Technicians often replace the auxiliary pump motor when the real fault is a corroded ground strap or a pin backed out of the connector, so always perform a voltage drop test under load before condemning the pump.
This code can set intermittently and leave no drivability complaint, especially if the vehicle rarely uses its auto start-stop feature, so a stored history code may be the only clue.
Transmission fluid that is overfilled or aerated can raise pump current draw enough to set P0B03 without any mechanical failure inside the pump.
Some vehicles share the auxiliary pump circuit with other low-current accessories, and a failing accessory can back-feed the circuit and mimic a pump phase fault.

Can I keep driving with P0B03?

You can usually drive the vehicle, but the auxiliary pump may be disabled, so the engine may not restart smoothly after an auto start-stop event and the transmission may feel rough at low speeds. Avoid heavy stop-and-go traffic and long idles until the fault is repaired, and do not tow or haul with the vehicle if the warning light is active.

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.