P0C1B: Auxiliary Transmission Fluid Pump Control Module Internal Temperature Too High

What it means

The auxiliary transmission fluid pump control module reports internal temperature above the protection threshold.

At a glance

• Usually lights the check-engine light
• The engine or gearbox may go into limp mode

How it works

The auxiliary transmission-fluid pump control module operates the pump that circulates fluid when the main transmission pump is not providing flow. It monitors its own internal temperature and sets P0C1B when that temperature exceeds its protection threshold, which can follow sustained pump load or high ambient heat.

Common causes

Most likely first.

1. Sustained pump load
2. Ambient temperature too high

Symptoms

• Check engine or transmission warning light on
• Harsh, delayed, or missing shifts
• Possible limp mode (locked in one gear)
• Slipping or shuddering during gear changes

How to diagnose it

1. Record freeze-frame data and check live pump-module temperature and pump command to see whether the high reading follows extended operation or high load.
2. Inspect the auxiliary pump module and transmission area for blocked airflow, heat exposure, fluid leaks, or damaged electrical connections.
3. Check transmission fluid condition and level using the manufacturer’s procedure, since low or degraded fluid can increase pump demand.
4. Check whether the auxiliary pump runs and circulates fluid when commanded, using the manufacturer’s diagnostic procedure.
5. If temperature remains high despite normal fluid condition and cooling, test the pump module and its temperature monitoring according to the manufacturer’s procedure.

Common fixes

• Correct low or degraded transmission fluid if confirmed by the manufacturer’s level and condition checks.
• Clear an obstruction or correct a cooling problem around the pump control module.
• Repair a pump wiring or connection fault that causes excessive load.
• Replace a failing auxiliary pump or control module if testing confirms the fault.

Can I keep driving?

Avoid continued driving if shifts become harsh, delayed, slipping, or the vehicle enters limp mode; transmission damage can worsen without adequate fluid circulation. Stop safely if drive is lost or the transmission warning escalates.