How to Jump Fuel Pump Relay on Chevy Truck: A Complete Step-by-Step Guide

Bottom line up front: If your Chevy truck cranks but won’t start, jumping the fuel pump relay is a quick diagnostic test that tells you whether the problem is the relay itself or the fuel pump. You connect a jumper wire between pin 30 and pin 87 in the relay socket, turn the ignition on, and listen for the fuel pump to run. If the pump runs when jumped, the relay is bad and needs replacement. If the pump doesn’t run, the issue is likely the fuel pump, wiring, or the control module.

What Is the Fuel Pump Relay and Why Does It Matter?

The fuel pump relay is an electrical switch that controls power to the fuel pump. When you turn the ignition key to the “ON” position, the truck’s Powertrain Control Module (PCM) sends a signal that closes the relay, allowing voltage to flow from the battery to the fuel pump. This primes the fuel system and keeps fuel pressure up while the engine runs. If the relay fails, the fuel pump won’t receive power, and your engine won’t start.

The fuel pump relay is typically located in the under-hood fuse box, often near the battery or on the driver’s side of the engine compartment. On some Chevy truck models, it may also be inside the interior fuse panel under the dashboard. Look for a small black relay labeled “FUEL PUMP,” “FP,” or “FUEL” on the fuse box cover or relay itself.

Recognizing the Symptoms of a Bad Fuel Pump Relay

Before you start jumping the relay, make sure the symptoms point to a relay problem. Common signs of a failing fuel pump relay include:

  • Engine cranks but won’t start: This is the most obvious symptom. Without power from the relay, the fuel pump cannot deliver fuel to the engine.
  • No humming or whirring noise from the fuel tank: When you turn the ignition on, the fuel pump should make a brief buzzing sound. If you don’t hear it, the relay may not be sending power.
  • Sudden stalling or hesitation while driving: A failing relay can lose contact intermittently, cutting power to the fuel pump and starving the engine of fuel.
  • Check Engine Light comes on: The PCM may detect fuel pressure or delivery issues and trigger codes like P0089 or P0191.
  • High gas mileage: A bad relay can cause the fuel pump to run erratically, leading to extra fuel being injected into the engine.

Tools and Materials You’ll Need

  • Jumper wire: A short piece of 12-14 gauge insulated wire with alligator clips or bare ends. A paper clip can work in a pinch.
  • Safety glasses: Protect your eyes from debris or sparks.
  • Wrench or ratchet set: For disconnecting the battery terminals if needed.
  • Multimeter (optional): To verify voltage and continuity.
  • Wiring diagram (optional): Helpful if you’re unsure about your specific relay pin layout.

Step-by-Step Guide: How to Jump the Fuel Pump Relay on a Chevy Truck

1. Disconnect the Negative Battery Terminal

Before doing any electrical work under the hood, always disconnect the negative battery cable. This prevents accidental shorts, sparks, and potential damage to the truck’s electrical system.

2. Locate the Fuel Pump Relay

Open the under-hood fuse box and find the fuel pump relay. It’s usually a small black cube with a diagram on top. If you’re having trouble, check your owner’s manual or look for a label on the fuse box cover. Common locations include near the battery or on the driver’s side firewall.

3. Remove the Fuel Pump Relay

Carefully pull the relay straight out of its socket using your fingers or a pair of pliers. Take note of the socket layout. You’ll see several pin slots labeled with numbers.

4. Identify Pins 30 and 87

Look at the relay itself or the socket diagram. The two terminals you need to connect are pin 30 (the power source from the battery) and pin 87 (the power output to the fuel pump). In most Chevy and GM trucks, these are the two pins that need to be bridged to bypass the relay.

Important: Do not jumper the coil control terminals (typically pins 85 and 86). Jumping the wrong pins can cause electrical damage.

5. Connect the Jumper Wire

Insert one end of your jumper wire into the socket slot for pin 30, and the other end into the slot for pin 87. Make sure the wire makes solid contact with the metal inside the socket. If you’re using a paper clip, bend it into a U-shape and insert both ends into the correct slots.

6. Reinstall the Fuel Pump Relay (Optional)

You can leave the relay out while testing, or you can push it back into the socket over the jumper wire. Either way works, but make sure the jumper wire stays securely in place.

7. Reconnect the Battery and Turn the Ignition On

Reconnect the negative battery terminal. Turn the ignition key to the “ON” position (do not start the engine). Listen carefully for the fuel pump. You should hear a buzzing or whirring sound coming from the fuel tank area, usually lasting for a couple of seconds. If you hear it, the fuel pump is getting power and is working properly.

8. Interpret the Results

  • If the fuel pump runs when jumped: The fuel pump itself is likely good. The problem is the relay, its control circuit, or the wiring between the relay and the PCM. Replace the fuel pump relay with a new one as a first step.
  • If the fuel pump does NOT run when jumped: The issue is elsewhere. Check the wiring from the relay socket to the fuel pump for damage, corrosion, or breaks. Also verify that the fuel pump has a good ground connection. If the wiring and ground check out, the fuel pump itself is likely faulty and needs replacement.

9. Remove the Jumper Wire

After testing, disconnect the jumper wire from the socket. Do not leave the jumper wire in place for extended driving, as it bypasses the relay’s safety function and can damage the fuel pump or electrical system.

10. Install a New Fuel Pump Relay

If the test confirmed the relay is bad, install a replacement relay with the same part number. Push it firmly into the socket until it clicks into place.

Alternate Method: Using a Copper Wire

If you don’t have jumper cables or alligator clips, you can use a 5-inch piece of copper wire with a half-inch of insulation stripped from both ends. After removing the relay, insert one stripped end into the upper left pin slot of the relay center, and the other end into the lower right pin slot. This connects the same two power terminals and sends power to the fuel pump. Test by turning the ignition on, then remove the wire once you’re done.

A Faster Diagnostic Trick: Swap the Relay

Before you start jumping wires, try this: Look in the fuse box for another relay with the same part number. Common candidates are the horn relay, A/C relay, or fog light relay – anything not needed for the engine to start. Swap that relay into the fuel pump relay socket. If the truck starts, you’ve confirmed the original relay is bad, and you can drive to the parts store to buy a replacement.

Common Causes of No Power to the Fuel Pump Relay

If jumping the relay doesn’t make the pump run, the problem may be one of these:

  • Blown fuse: Check the fuel pump fuse in the fuse box.
  • Faulty wiring: Look for broken, corroded, or loose connections between the relay socket and the fuel pump.
  • Bad fuel pump control module: The PCM or ECM may not be sending the signal to the relay.
  • Failed fuel pump: The pump itself may be worn out or seized.
  • Ignition switch failure: The switch may not be sending power to the relay circuit.

Safety Precautions

  • Always disconnect the battery before working on the relay socket.
  • Work in a well-ventilated area. Gasoline fumes are flammable and harmful to inhale.
  • Do not smoke or have open flames nearby.
  • Never leave the jumper wire in place for more than a quick test. Continuous bypass can overheat the fuel pump and cause damage.
  • If you’re not comfortable with electrical work, consult a professional mechanic.

Why Choose KEMSO Fuel Pumps for Your Chevy Truck

If you’ve determined that your fuel pump needs replacement, look no further than KEMSO. KEMSO fuel pumps are high-performance, OEM replacement products designed to meet or exceed the original factory specifications. Every KEMSO fuel pump comes with a lifetime warranty, giving you confidence that your repair is built to last. Whether you’re driving a Chevy Silverado, Suburban, Tahoe, or any other GM truck, KEMSO has the right fuel pump for your vehicle.

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Final Thoughts

Jumping the fuel pump relay on a Chevy truck is a straightforward diagnostic procedure that anyone with basic mechanical skills can perform. It helps you quickly determine whether the relay or the fuel pump is the problem, saving you time and money on unnecessary repairs. Remember, jumping the relay is a temporary test – not a permanent fix. If the test shows the relay is bad, install a new one. If the pump doesn’t run, check the wiring and ground, and consider replacing the fuel pump with a reliable, high-quality part like those from KEMSO.

For more information on fuel pump replacement and to browse the full line of KEMSO fuel pumps backed by a lifetime warranty, visit https://www.kemsoracing.com/


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