What it means
The second auxiliary transmission fluid pump cannot maintain pressure even at high duty cycle. Indicates internal hydraulic leakage downstream of the pump.
At a glance
- Usually lights the check-engine light
How it works
Auxiliary transmission fluid pump B supplies hydraulic pressure to the transmission when the system calls for it. The control module monitors pump operation and pressure response; this code sets when pump B cannot maintain the expected pressure despite being driven hard, suggesting fluid is escaping downstream or through a bypass.
Common causes
Most likely first.
- Worn or hardened seals downstream of pump
- Pressure relief or bypass valve stuck open
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
- Read freeze-frame data and scan-tool transmission pressure and pump B command data to establish when pressure fell short and whether the pump was being driven.
- Check the transmission fluid level and condition using the vehicle's specified procedure, and inspect for leaks that could contribute to low hydraulic pressure.
- Inspect pump B's wiring, connector, and fluid-line connections for damage, looseness, or leakage before attributing the fault to an internal leak.
- Compare commanded pump B operation with measured pressure using the vehicle's specified test procedure to confirm that pressure remains low as command increases.
- If the pump circuit and supply are sound, have the downstream seals and pressure-relief or bypass valve checked for internal leakage.
Common fixes
- Correct the fluid level or address an external leak using the manufacturer's specified fluid and procedure.
- Repair damaged pump B wiring or connector connections if they prevent normal pump operation.
- Replace failed downstream seals that allow hydraulic pressure to escape.
- Free or replace a pressure-relief or bypass valve that is stuck open.
- Repair or replace pump B only if testing shows it cannot produce pressure and downstream leakage has been ruled out.
Can I keep driving?
Avoid driving if shifts are delayed, harsh, slipping, or missing; stop safely if the transmission loses drive or enters a restricted gear. Continued operation with inadequate hydraulic pressure can worsen clutch and transmission damage.
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.