What it means
The second 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 B circulates transmission fluid when the TCM requests extra flow, and the module monitors whether the pump switches off when that request ends. This code sets when pump B continues running with no active command.
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 live pump B command status and related transmission codes to confirm when the unwanted running occurs.
- With the vehicle safely parked, verify whether pump B keeps running while the scan tool shows it is uncommanded.
- Inspect pump B's control wire and connector for chafing, moisture, or contact with a permanent B+ supply.
- Measure the uncommanded control circuit for unwanted voltage and compare it with the manufacturer's specification.
- If the wiring is sound, inspect pump B for carbon or debris that prevents free movement and check whether the TCM output remains active.
Common fixes
- Repair pump B control wiring shorted to permanent power.
- Clean and secure corroded or loose pump B connector terminals.
- Remove debris or carbon that is preventing pump B from switching off.
- Repair or replace the TCM if its pump B output driver remains active after wiring faults are ruled out.
Can I keep driving?
Avoid driving if shifts slip, shudder, or become harsh or delayed, or if the transmission enters limp mode, because continued operation can worsen damage. If shifting is 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.