What it means
The first auxiliary transmission fluid pump runs even when no command is active.
At a glance
- Usually lights the check-engine light
How it works
Auxiliary pump A circulates transmission fluid when the transmission needs extra hydraulic flow, and the transmission control module (TCM) switches and monitors its operation. This code sets when the TCM detects pump A running while it has not commanded the pump on.
Common causes
Most likely first.
- TCM output driver stuck on
- Control wire shorted to a permanent B+ supply
- Carbon or debris buildup preventing free movement
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
- Record freeze-frame data and check transmission codes and live pump-command status to see when the unwanted operation was detected.
- With the vehicle safely parked, check whether pump A continues running when the scan tool shows no command, and listen for its operation.
- Inspect pump A's connector and control-wire harness for damage, chafing, moisture, or a wire touching a permanent power supply.
- Check the pump A control circuit for unwanted voltage with the pump uncommanded, and trace any voltage back toward the power source.
- If wiring is intact, test the pump A motor for free movement and debris, then check whether the TCM output remains active when it should be off.
Common fixes
- Repair chafed or shorted pump A control wiring.
- Clean and secure corroded or loose pump A connector terminals.
- Remove debris or carbon that is preventing pump A from switching off freely.
- Repair or replace the TCM if its pump A output driver stays on after circuit faults are ruled out.
Can I keep driving?
Avoid driving if shifts are slipping, shuddering, harsh, or delayed, or if the transmission enters limp mode; continued driving can worsen transmission damage. If shifting remains normal, limit driving and arrange diagnosis soon.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.