Short to voltage in the pump motor supply circuit; Faulty electric/auxiliary transmission fluid pump motor; Damaged or corroded wiring harness or connectors; Failed transmission control module (TCM) or power control module; Blown fuse or faulty relay supplying the pump motor; Poor ground connection for the pump motor circuit

DTC codes / P0Bxx · Hybrid propulsion / P0B0B

P0B0BElectric/Auxiliary Transmission Fluid Pump A Motor Supply Voltage Circuit High

P0B0B indicates that the transmission control module has detected an abnormally high voltage on the power supply circuit feeding the electric or auxiliary transmission fluid pump motor. This typically means the pump motor is receiving voltage above the expected range, which can be caused by a short to power, a faulty pump, or a wiring issue.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaHybrid propulsion

Symptoms you may notice

Illumination of the check engine light or transmission warning light
Often no symptoms besides the warning light
Transmission may enter limp mode or fail to shift properly
Overheating of the transmission fluid due to pump malfunction
Delayed engagement or slipping gears
In some cases, the vehicle may stall or hesitate during acceleration

Common causes, most likely first

Short to voltage in the pump motor supply circuit
Faulty electric/auxiliary transmission fluid pump motor
Damaged or corroded wiring harness or connectors
Failed transmission control module (TCM) or power control module
Blown fuse or faulty relay supplying the pump motor
Poor ground connection for the pump motor circuit

How to diagnose and fix it

Use a scan tool to verify the code and check for related codes in the transmission control module
Inspect the wiring harness and connectors for damage, corrosion, or loose pins
Measure voltage on the pump motor supply circuit with a multimeter to confirm high voltage
Check the pump motor relay and fuse for proper operation
Test the pump motor by applying power directly and observing operation
If voltage is high, trace the circuit for shorts to power and repair as needed
Replace the pump motor or TCM if diagnostics indicate internal failure

Don't overlook the simple electrical checks

A shorted pump motor can back-feed voltage into the supply circuit, causing a high voltage code even when the TCM is functioning correctly.
Corroded connectors or chafed wires often mimic a failed pump motor, so always perform a thorough visual inspection before replacing parts.
The code may set intermittently due to vibration or temperature changes, so wiggle-testing the harness while monitoring live data can reveal the fault.
A weak battery or charging system issue can cause voltage spikes that trigger this code, so check the vehicle's overall electrical health first.
Some vehicles use the auxiliary pump only during auto start-stop events, so the code may not affect normal driving until that feature activates.

Can I keep driving with P0B0B?

It is generally safe to drive with this code if the transmission behaves normally, but avoid heavy loads or aggressive driving that could overheat the transmission. If the transmission enters limp mode or you notice slipping, stop driving and seek professional diagnosis.

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.