A fuel pump relay is an important component in a vehicle’s fuel delivery system. It is essentially a switch that controls power to the fuel pump. The fuel pump relay receives signals from the engine computer and turns the fuel pump on when the engine is cranked or running. If there is a problem with the fuel pump relay, it can cause issues with the fuel pump and prevent the engine from starting or running properly.
Causes of Fuel Pump Relay Faults
There are several potential causes for a faulty fuel pump relay:
- Faulty relay contacts – The relay has electrical contacts inside that can wear out over time. This can prevent the relay from closing properly to turn the fuel pump on.
- Bad relay coil – The coil is what receives voltage from the engine computer to activate the relay. A damaged coil will not allow the relay to function.
- Blown fuse – There is usually a fuse that provides power to the fuel pump relay. If this fuse is blown, it will cut off power to the relay.
- Faulty engine computer – Issues with the computer can prevent it from properly signaling the relay to turn on.
- Damaged relay wiring – Broken or corroded wires leading to the relay can cause connection problems.
Diagnosing a Fuel Pump Relay Fault
If you suspect an issue with the fuel pump relay, here are some steps to diagnose the problem:
- Check the relay fuse – Locate the fuse for the fuel pump relay in the fuse box and make sure it is not blown.
- Check for power at the relay – Use a multimeter to check for 12V at the relay connector when the key is on. No power indicates a wiring issue.
- Check the relay ground – Verify the ground circuit from the relay to the vehicle chassis is intact.
- Check for computer signals – Check that the relay is receiving turn-on and turn-off signals from the engine computer during cranking and running.
- Perform a relay resistance test – Remove the relay and use a multimeter to check continuity between terminals when energized.
- Listen for fuel pump prime – Turn the key on and listen for a momentary whine or hum from the fuel pump at the rear of the vehicle.
- Check for voltage at fuel pump – Use a multimeter to check for power at the fuel pump connector with the relay energized.
Fuel Pump Relay Fault Codes
If there is a problem with the fuel pump relay, the engine computer may set a diagnostic trouble code (DTC) to indicate the issue. Here are some common fuel pump relay-related codes:
P0230 – Fuel Pump Primary Circuit
This code indicates an issue with the electrical circuit that controls the primary fuel pump relay. Potential causes include:
- Faulty fuel pump relay
- Blown fuse for fuel pump relay
- Broken or shorted wiring to relay
- Bad electrical connection at relay
P0627 – Fuel Pump Control Circuit Open
This code sets when the PCM detects an open circuit in the fuel pump relay control circuit. Potential causes include:
- Faulty fuel pump relay
- Loose or corroded wiring connector
- Open circuit wire to relay coil
- Bad ground connection
P0628 – Fuel Pump Control Circuit Low
This code indicates low system voltage on the fuel pump relay control circuit. It could be caused by:
- Weak battery
- Faulty alternator
- Short to ground in relay control wire
- Damaged PCM output circuit
P1233 – Fuel Pump Driver Module Disabled
This indicates the PCM has intentionally disabled the fuel pump relay control circuit due to some system fault. Potential causes include:
- Engine overheating condition
- Vehicle speed sensor failure
- VIN misconfiguration
- Open or short in fuel pump control circuit
Replacing the Fuel Pump Relay
If diagnostics indicate a bad fuel pump relay, it will need to be replaced. Here is the general procedure:
- Locate the fuel pump relay – Usually found in the fuse box under the hood or dashboard.
- Remove electrical connector – Disconnect the wiring harness from the relay.
- Remove relay – Take out the retaining bolt or clip and remove from bracket.
- Install new relay – Push relay into socket until it clicks and locks.
- Reconnect connector – Plug wiring harness back into relay.
- Check operation – Turn key on and listen for fuel pump prime.
Be sure to get an identical replacement relay that matches the original. Consult a vehicle repair manual for the proper relay and installation procedure for your specific vehicle.
Fuel Pump Relay Precautions
- Do not tap or strike the relay during testing. This can damage the internal contacts.
- Make sure the battery is disconnected before doing any relay removal or replacement.
- Never force a relay into the socket. It should click smoothly into place.
- Don’t ignore fuel pump relay issues. A no-start condition may occur if it fails completely.
- Don’t improvise or use the wrong relay. It may overheat, not function properly or cause other issues.
The fuel pump relay is an essential component that allows power to reach the fuel pump when the vehicle is cranked or running. Problems with the relay or related circuits can prevent fuel delivery, causing a no-start or stall condition. Diagnosing the issue requires electrical testing of the relay fuse, power and ground circuits, PCM signals, and the relay itself. Set diagnostic trouble codes can also help pinpoint causes. Replacing a faulty fuel pump relay with a new equivalent part is usually required to restore normal engine operation and fuel pump function.
|Fuel Pump Relay Fault Code
|Fuel Pump Primary Circuit Fault
|Faulty relay, blown fuse, wiring issue
|Fuel Pump Control Circuit Open
|Faulty relay, loose/corroded connector, open circuit wire
|Fuel Pump Control Circuit Low
|Weak battery, faulty alternator, short to ground
|Fuel Pump Driver Module Disabled
|Engine overheat, speed sensor failure, VIN misconfiguration
This table summarizes some common fuel pump relay related fault codes, the circuit descriptions, and potential causes to investigate.