P27E1: Electric/Auxiliary Transmission Fluid Pump A Pressure Too Low

What it means

Electric/auxiliary transmission fluid pump A is producing pressure below the expected level.

At a glance

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

How it works

Electric or auxiliary transmission fluid pump A supplies hydraulic pressure when the transmission control system calls for it. The module compares the pressure associated with pump A against the expected level and sets P27E1 when that pressure is too low, which can result from low fluid or a worn or internally leaking pump.

Common causes

Most likely first.

1. Pump worn or leaking internally
2. Transmission fluid level low

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 transmission data for pump A operation and pressure when the fault sets, noting whether pump B or other pressure faults are also present.
2. Check the transmission fluid level and condition using the vehicle manufacturer's specified procedure, since an incorrect level can reduce pump A pressure.
3. Inspect the pump A area and transmission for fluid leaks that could account for a low level or pressure.
4. Use a scan tool to command or observe pump A operation and compare its reported pressure with the manufacturer's expected data.
5. If fluid level and external leaks do not explain the reading, test pump A and its hydraulic circuit for internal wear or leakage using the manufacturer's procedure.

Common fixes

• Correct the transmission fluid level with the specified fluid and procedure.
• Repair fluid leaks contributing to low level or pressure.
• Replace pump A if testing confirms it is worn or leaking internally.
• Repair the hydraulic passage or seal causing internal pressure loss if testing identifies one.

Can I keep driving?

Avoid driving if shifts are slipping, missing, or the transmission enters limp mode; low pump A pressure can quickly damage clutches and other transmission parts. Arrange prompt diagnosis, and stop if the vehicle loses drive or cannot shift safely.