What it means
Voltage on the second fuel pump control line is above the expected window. Typical causes are a short to battery or an open motor winding.
At a glance
- Usually lights the check-engine light
How it works
Fuel Pump B is the secondary fuel pump stage, and its control module monitors the voltage used to operate it. P2634 sets when the control-circuit voltage is above the expected window, commonly because the wire is shorted to battery voltage or an open pump winding prevents the expected load.
Common causes
Most likely first.
- Control wire shorted to B+
- Open motor winding
- Connector pins corroded - high contact resistance
Symptoms
- Check engine light on
- Hard start, no start, or stalling under load
- Power loss especially at high load or rpm
- Possible long cranking time
How to diagnose it
- Record freeze-frame data and check for related Pump B, fuel-pressure, and electrical codes.
- Inspect Pump B connectors and wiring for corrosion, loose pins, or a control wire touching a battery-positive supply.
- Use the wiring diagram to identify the control circuit and check for unwanted battery voltage with the pump and relay isolated as specified.
- Command Pump B on if supported and test circuit voltage and pump current against the manufacturer's specification.
- If no wiring short is found, test the pump winding for an open circuit and verify relay and module-driver operation.
Common fixes
- Repair a loose or corroded Pump B connector.
- Repair a control wire shorted to battery voltage.
- Replace Pump B if its winding is open.
- Replace a failed relay or module driver only after confirming the pump and wiring are sound.
Can I keep driving?
If starting is difficult or the engine stalls or loses power, avoid driving in situations where sudden loss of power would be hazardous. Have it towed if it cannot maintain steady operation, since the secondary pump may not deliver fuel.
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.