A failing pump relay affects your vehicle’s ability to pump fuel, which prevents it from starting. If you are not able to fix or replace the fuel pump relay immediately, you can bypass the relay to be able to use your car. Keep reading to learn how to jump a fuel pump relay.
Is it safe to bypass a fuel pump relay?
Before learning the process of bypassing a bad fuel pump relay, let’s explore how a fuel pump relay works—the fuel pump relay powers the fuel pump, which is supplies by the vehicle’s powertrain control module. Once you turn on your car, the PCM turns on the fuel pump by energizing the fuel pump relay.
The fuel pump relay then closes its circuit, allowing the fuel pump to pump fuel into the engine. When the fuel pump relay is damaged, it is unable to complete its circuit, thereby preventing the transfer of power to the fuel pump.
The fuel pump relay also acts as a timer for the fuel pump. It features a timer that pre-pressurizes the fuel system when you turn on the car. Bypassing the pump relay can lead to fuel being pumps at high pressure.
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This can end up damaging components of your car, such as the fuel pump. As such, it is not advisable to drive the vehicle with the bypassed fuel pump relay. A damaged fuel pump is more expensive to replace than fixing or replacing a fuel pump relay.
How to jump a fuel pump relay
Jumping the relay means diverting power via an electrical conductor from the relay directly into the fuel pump. All you need is a metal conductor to transfer the electric current from the PCM to the fuel pump.
Steps for jumping the fuel pump relay
- Ensure your car is parked on flat ground and before you get started.
- Then open the hood and look for the relay center. It is usually located on the right side of the engine compartment, behind the driver’s side headlamp.
- The pump relay is in a black plastic box that contains all the vehicle’s relays.
- Remove the cover from the under-hood relay center.
- Use the diagram on the cover to locate the fuel pump relay.
- Then remove the 4-pin fuel pump relay from the relay center.
- Take a 5-inch length of small-diameter copper wire and strip approximately 1/2 inch of the insulation from each end with a wire stripper.
- Insert one end of the copper wire into the upper-left pin slot of the 4-pin receptacle where the fuel pump relay plugs into the relay center.
- And insert the other end of the wire into the lower-right pin slot of the 4-pin receptacle where the fuel pump relay plugs into the relay center.
- Then turn on the vehicles and see if it works.
- If both ends of the wire are correctly seated, the fuel pump will turn on.
How to tell if a fuel pump relay is bad
In most cases, people do not realize their fuel pump relays are damaged until the car refuses to turn on. Here are some simple ways to diagnose a bad fuel pump relay;
The check engine light is on.
When the fuel pump relay starts failing, the fuel pressure may get affected, which in turn causes the fuel pressure sensor to note a wrong value. The ECU will store a trouble code for the failing fuel pressure causing the engine light to turn on.
Additionally, a faulty pump relay may also lead to a voltage spike in the relay. This is due to a blown fuse, shorted fuel pump, frayed wiring, or a blown circuit. The ECU will interpret the voltage reading as an error code and cause the engine light to turn on.
Rough acceleration
A damaged pump relay will affect the fuel pump’s pressure, which affects the amount of fuel being pumped into the combustion chamber as such acceleration may get affected due to the intermittent fuel injection.
Stalling or idling engine
Damaged soldering on the fuel pump relay may affect electrical connectivity. The power supplied to the fuel pump will, in turn, be inconsistent. This may lead to intermittent fuel supply leading to a stalling or idling engine.
No noise from the fuel pump
The fuel pump produces a whirring noise once you turn on the ignition. This is due to building fuel pressure in the fuel rail. A quiet fuel pump is a sign of a failing fuel pump relay as the relay timer is not controlling the fuel pressure.
The engine is dead
This is the ultimate sign of a failing fuel pump relay. An incomplete circuit will prevent fuel pump operation, thereby preventing the engine from starting due to lack of fuel in the combustion chambers.
Longer starting time
Cause the failing circuit, which may take a while to complete or get completed intermittently, affects fuel pressure. This means the engine will take time to get enough fuel to start the car.
High mileage
Lack of fuel pressure regulation may lead to increased fuel injection into the engine, leading to higher fuel consumption.
The car dies while you are driving.
As a result of disrupted fuel supply to the vehicle’s engine.
Fuel Pump Relay Diagnosis
This process helps to determine if there is electrical continuity.
- Locate the fuse box and locate the fuel pump relay
- Lift it and check under it for the numbers 30, 85, 86, and 87. If you find these numbers, you can put the fuel pump relay back.
- Put the relay back so you can reach the pins with a multimeter while you cycle the ignition.
- Turn on the ignition and check pin 87 with a multimeter. Voltage means the relay is working. Intermittent voltage means bad relay circuitry.
- If you do not get voltage, check to see if you will get constant voltage on Pin 30 with the ignition on. If you don’t get voltage, there might be a broken fuse.
- Ensure you have constant voltage on pin 85 and pin 86. They should be grounded from the engine control unit when you turn on the ignition.
- If you have any continuity problems, remove the case from it to check for any bad soldering.
- Resolder the relay if you find any problems.
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Fuel Pump Relay Replacement Cost
- The fuel pump relay can be bought online or at your local spare parts store. The price should range from $75-$250 depending on the car. Additional costs related to fuel pump relay replacement include labor costs. The average cost of the fuel pump relay replacement will range between $90 and $250.
- This is dependent on the mechanic’s charging method, which can either be hourly or per job pay rate.
- A mechanic will take between One and Six hours depending on the mechanic’s expertise, the car’s layout and the tools at hand