The fuel pump shut off switch is designed to disengage the power to the fuel pump when a vehicle comes to an instant stop. Most vehicles today have an inertia switch near the main air bag module with a reset button. If the fuel pressure switch turns off the power to the fuel pump during normal vehicle operation, then the reset button can be pressed to reset the switch and resume power to the fuel pump.
The fuel cut-off switch is a safety reset switch which starts the fuel pump and allows gas flow to the engine. If you get hit and it is only a minor fender-bender, the fuel pump may shut off; you will know when you try to start the car again and the engine just turns but doesn’t start.
At this point, just hit the reset button and you’re on your way. In the event of a major collision, where the gas line is ruptured, it prevents the fuel pump from spewing gas continuously and increasing the chances of fire or explosion. All vehicles have a reset switch, but most of them need a dealer to access it after a collision.
It works much like a circuit breaker in your home. If you blow a circuit at home, you can go to the circuit-breaker box and push in the red button or toggle the lever from off to on to reset that circuit.
Part 1 of 5: Knowing the signs of failure
If your vehicle drives normally and then all of a sudden the engine shuts off and does not restart, the fuel pump shut off switch may have tripped. Sometimes the fuel pump shut off switch may toggle on and off repeatedly, making the engine sound like it is having an issue with a fuel regulator.
If the fuel pump shut off switch fails, the engine management system records this event. A fuel pressure sensor lets the computer know of a decrease more than five psi (pounds per square inch). The fuel pump shut off switch is wired from the battery to the ignition switch to the vehicle’s computer and to the fuel pump. If the switch loses communication from any part of the vehicle, the switch activates.
There are several engine light codes associated with the fuel pump shut off switch:
Part 2 of 5: Verifying the fuel pump shut off switch condition
Step 1: Turn the key to run position. Locate the reset button to the fuel pump shut off switch.
Press and hold the reset button for about 20 seconds.
- Note: The fuel pump shut off switch reset button is usually located either under the dash in the driver compartment or under the driver or passenger seat. Just move the seat forward and pull back on the carpet or popping off the cover under the seat to access the switch.
Step 2: Attempt to start the engine. If the switch is defective, the engine will not start up.
However, if the switch is resetting itself, then the engine will start up and then shut off.
Part 3 of 5: Replacing the fuel pump shut off switch
- Allen wrench set
- Boxed end wrenches
- Electrical cleaner
- Flathead screwdriver
- Ratchet with metric and standard sockets
- Torques bit set
- Wheel chocks
Step 1: Park your vehicle on a flat, hard surface. Make sure that the transmission is in park (for automatics) or in 1st gear (for manuals).
Step 2: Place wheel chocks around the rear tires. In this case, the wheel chocks go around the front tires since the rear of the vehicle will be lifted up.
Engage the parking brake to the lock the rear tires from moving.
Step 3: Install a nine volt battery saver into your cigarette lighter. This keeps your computer live and your settings currently in the vehicle.
If you do not have a nine volt battery saver, that is ok.
Step 4: Open the vehicle’s hood to disconnect your battery. Take the ground cable off of the battery’s negative post disabling the power to the fuel pump and sending unit.
If your switch is under the dash:
Step 5: Locate the fuel pump shut off switch under the dash. Remove the harness attached to the switch.
Remove the mounting hardware securing the switch to the firewall or bracket under the dash.
Step 6: Remove the fuel pump shut off switch. Use electrical cleaner and clean the contacts on the harness to the switch.
Step 7: Install the switch. Secure it with the mounting hardware.
Step 8: Connect the harness to the switch.
If the switch is located behind the driver or passenger seat:
Step 9: Slide the seat forward all the way. Pull back on the carpet overlapping behind the seat.
You may need to remove some panels or stripping along the side of the cab to remove the carpet.
Step 10: Locate the fuel pump shut off switch under the dash. Remove the harness attached to the switch.
Remove the mounting hardware securing the switch to the floor board.
Step 11: Remove the fuel pump shut off switch. Use electrical cleaner and clean the contacts on the harness to the switch.
- Note: You may have to remove a cover to get to the switch. The cover may be mounted by tabs or screws.
Step 12: Install the switch. Secure it with the mounting hardware.
Step 13: Connect the harness to the switch.
- Note: If you had to remove any carpet, be sure to put the carpet back and any panels or stripping that secures the carpet in place.
Step 14: Slide the seat back into the position it was originally set for.
Part 4 of 5: Checking for proper functionality
Step 1: Reconnect the battery. Reconnect the ground cable back onto the battery’s negative post.
Remove the nine volt battery saver from the cigarette lighter.
- Note: If you did not have a nine volt battery saver, you will have to reset all of the settings in your vehicle, like your radio, electric seats, and electric mirrors. If you had a nine volt battery saver, you will need to clear the engine codes if any before starting the vehicle up.
Step 2: Tighten the battery clamp up tight. Ensure that the connection is good.
Step 3: Turn the ignition key on. Listen for the fuel pump to activate and turn off the ignition after the fuel pump stops making noise.
- Note: You will need to cycle the ignition key on and off 3 to 4 time to ensure all the fuel rail is full of fuel.
Step 4: Start the engine. Start the engine up and check to make sure that the engine will stay running.
Step 5: Remove the wheel chocks from the rear wheels. Put these aside.
Part 5 of 5: Test drive the vehicle
Step 1: Drive the vehicle around the block. During the test, feel for any symptoms of the fuel cutting out.
Also, accelerate the engine quickly to make sure that the fuel pump is working correctly.
Step 2: Monitor the dash for any engine lights.
If your engine light comes on after replacing the fuel pump shut off switch, then there may be further diagnosis of the fuel pump assembly needed or a possible electrical issue within the fuel system. If the problem persists, then have one of YourMechanic’s certified mechanics inspect the fuel pump shut off switch and perform a replacement.
This article originally appeared on YourMechanic.com as How to Replace a Fuel Pump Shut Off Switch and was authored by Marvin Sunderland.