Low or degraded transmission fluid causing the auxiliary pump to work harder and overheat.; A failing auxiliary transmission fluid pump motor that draws excessive current and generates extra heat.; Restricted or blocked transmission fluid cooler lines or a clogged cooler, reducing heat dissipation.; A faulty temperature sensor inside the auxiliary pump control module, sending an inaccurate high reading.; Internal damage or degradation of the auxiliary pump control module itself, such as failed thermal protection circuitry.; Poor electrical connections or damaged wiring to the auxiliary pump, causing voltage drops and increased current draw.; A software calibration issue in the control module that misinterprets temperature data under certain conditions.

DTC codes / P0Cxx · Hybrid propulsion / P0C1B

P0C1BElectric/Auxiliary Transmission Fluid Pump Control Module Internal Temperature Too High

P0C1B indicates that the electric auxiliary transmission fluid pump control module has reported an internal temperature that exceeds its safe operating limit. The computer detected this by monitoring a temperature sensor inside the control module and setting the code when the reading stayed above a calibrated threshold for a set period.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyProfessional

AreaHybrid propulsion

Symptoms you may notice

Illumination of the malfunction indicator lamp (MIL) on the dashboard.
Often no symptoms besides the warning light, especially if the fault is intermittent.
Reduced or absent auxiliary transmission fluid pump operation, which may affect cooling and lubrication during engine stop-start events.
Possible transmission overheating or poor shift quality under heavy load or during stop-start driving.
In some vehicles, the powertrain control module may disable the engine auto-stop feature to protect the transmission.

Common causes, most likely first

Low or degraded transmission fluid causing the auxiliary pump to work harder and overheat.
A failing auxiliary transmission fluid pump motor that draws excessive current and generates extra heat.
Restricted or blocked transmission fluid cooler lines or a clogged cooler, reducing heat dissipation.
A faulty temperature sensor inside the auxiliary pump control module, sending an inaccurate high reading.
Internal damage or degradation of the auxiliary pump control module itself, such as failed thermal protection circuitry.
Poor electrical connections or damaged wiring to the auxiliary pump, causing voltage drops and increased current draw.
A software calibration issue in the control module that misinterprets temperature data under certain conditions.

How to diagnose and fix it

Verify the code with a scan tool and check for any related codes in the transmission control module (TCM) or powertrain control module (PCM).
Inspect the transmission fluid level and condition; top off or replace fluid if it is low, dark, or contaminated.
Check the auxiliary pump electrical connector and wiring for corrosion, loose pins, or damage; repair as needed.
Test the auxiliary pump motor for excessive current draw or abnormal resistance using a multimeter or oscilloscope.
Inspect the transmission fluid cooler and lines for restrictions or blockages; flush or replace components if necessary.
Use a scan tool to monitor the auxiliary pump control module temperature sensor data and compare it with actual fluid temperature to identify sensor drift.
If all external checks pass, follow the manufacturer's diagnostic flow for internal control module faults, which may require module replacement or reprogramming.

Overheating Pump Module Isn't Always the Module

A low transmission fluid level is a commonly overlooked cause because the auxiliary pump runs dry and overheats, yet the fluid leak may be external and easily missed.
The temperature sensor inside the control module can fail and report a false high temperature, leading to unnecessary module replacement when only the sensor is at fault.
Restricted cooler lines often set this code without any visible leak, and the restriction is only found by checking flow or pressure.
In some vehicles, the auxiliary pump only runs during engine auto-stop, so the code may not set during a short test drive and requires specific enable criteria to reproduce.
This code does not always mean the module is permanently damaged; intermittent electrical faults can cause temporary high temperature readings that clear after repair.

Can I keep driving with P0C1B?

It is generally safe to drive with this code as long as the transmission is not overheating or slipping, but avoid heavy loads, trailer towing, and prolonged stop-and-go traffic until the fault is repaired. If the transmission temperature warning illuminates or performance degrades, stop driving and seek service immediately.

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.