What it means
Voltage on the second fuel pump control line is below the expected window. Usually a short to ground or a shorted motor winding.
At a glance
- Usually lights the check-engine light
How it works
Fuel Pump B is the secondary fuel pump stage, and the control module monitors voltage on the circuit that operates it. P2633 sets when that circuit voltage is below the expected window, often because the control wire is grounded or the Pump B motor winding is shorted.
Common causes
Most likely first.
- Control wire shorted to ground
- Internal short in pump motor
- 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 other Pump B, fuel-pressure, or low-voltage codes before testing the circuit.
- Inspect Pump B wiring and connectors for chafing to ground, corrosion, loose pins, or heat damage.
- Use the wiring diagram to identify the Pump B control wire and check it for a short to ground with the circuit safely isolated as specified.
- Command Pump B on if supported and compare control voltage and pump current with the manufacturer's specification.
- If the wiring is not grounded, test the pump motor winding and relay or driver circuit to locate a shorted component.
Common fixes
- Clean or repair corroded or damaged Pump B connector pins.
- Repair a control wire shorted to ground.
- Replace Pump B if its motor winding is internally shorted.
- Replace a faulty relay or module driver only after verifying the pump and wiring.
Can I keep driving?
Do not rely on the vehicle for a long trip if it has hard starts, stalls, or loses power under load; Pump B may not deliver fuel reliably. Avoid heavy acceleration and stop driving if the engine begins to stall.
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.