Fuel Pump "B" Control Circuit Low
Code P2633 indicates the fuel pump B control circuit is detecting a low voltage condition. The engine control module is unable to properly command the secondary fuel pump, which can prevent fuel delivery and cause starting or running issues.
What You Might Notice
- Check engine light is illuminated
- Engine won't start or has difficulty starting
- Engine misfire or stalling during operation
- Engine cranks but does not start
- Reduced fuel economy or engine dies at operating temperature
Most Common Causes
- 1
Fuel pump B circuit wiring fault
Damaged, corroded, or disconnected wiring in the fuel pump B control circuit. Check for loose connectors, broken wires, or poor grounds that cause voltage loss.
- 2
Fuel pump relay failure
The relay controlling fuel pump B is not switching properly or is stuck open, preventing current flow to the fuel pump motor.
- 3
Fuel pump B motor failure
The secondary fuel pump has internal resistance or is failing, drawing insufficient current and creating a low voltage signal in the control circuit.
- 4
Engine control module programming or connector issue
A faulty ECM connector, loose pin, or outdated software can cause incorrect voltage readings on the fuel pump B control circuit.
How to Diagnose It
- 1
Check Fuel pump B circuit wiring fault — Damaged, corroded, or disconnected wiring in the fuel pump B control circuit. Check for loose connectors, broken wires, or poor grounds that cause voltage loss.
- 2
Check Fuel pump relay failure — The relay controlling fuel pump B is not switching properly or is stuck open, preventing current flow to the fuel pump motor.
- 3
Check Fuel pump B motor failure — The secondary fuel pump has internal resistance or is failing, drawing insufficient current and creating a low voltage signal in the control circuit.
- 4
Check Engine control module programming or connector issue — A faulty ECM connector, loose pin, or outdated software can cause incorrect voltage readings on the fuel pump B control circuit.
How to Fix It
- 1
Inspect and repair fuel pump B wiring
Visually inspect the fuel pump B control circuit wiring harness for damage, corrosion, or loose connections. Repair or replace any damaged wiring, clean corroded connectors, and ensure all grounds are secure.
- 2
Test and replace fuel pump relay
Use a multimeter to test the fuel pump B relay for proper switching. If the relay fails the test or shows resistance, replace it with a new OEM relay.
- 3
Replace fuel pump B motor
If wiring and relay test good, the secondary fuel pump is likely failing. Remove and replace the fuel pump B assembly with a new or remanufactured unit.
- 4
Check ECM connector and reprogram
Inspect the engine control module connector for loose pins or corrosion. Clean contacts and reseat the connector. If the issue persists, update ECM software or replace the module if faulty.
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