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

The bottom line: If your Chevy truck cranks but won't start, the fuel pump relay is often the culprit. Bypassing the fuel pump relay is a temporary fix that sends power directly to the fuel pump, allowing you to start the truck and diagnose the real problem. This is not a permanent repair, but it can get you back on the road quickly. The process involves locating the relay in the fuse box, removing it, and using a jumper wire to connect the power source terminal to the fuel pump terminal, typically pins 30 and 87 .

What Is a Fuel Pump Relay and Why Does It Fail?

The fuel pump relay is an electrical switch that controls power to the fuel pump. When you turn the ignition key, the Powertrain Control Module (PCM) sends a signal to the relay, which then allows voltage to flow to the fuel pump. The pump primes the fuel system and keeps fuel pressure up while the engine runs .

A failed relay means the fuel pump gets no power, and your engine won't start. Common causes of relay failure include age, corrosion, overheating, and electrical shorts. Symptoms of a bad fuel pump relay include:

  • Engine cranks but won't start
  • Engine stalls while driving
  • Rough acceleration
  • Check engine light comes on
  • No sound from the fuel pump when you turn the key to the ON position

Tools and Materials You Need

Before you start, gather these items:

  • Jumper wire – A short length of insulated 12-14 gauge wire with alligator clips or bare ends. You can also use a paperclip in a pinch
  • Safety glasses – Protect your eyes from sparks or debris
  • Multimeter (optional) – To verify voltage and continuity
  • Socket wrench or screwdriver – To access the fuse box and remove the relay if needed
  • Owner's manual – Helps locate the relay and identify terminals

Step-by-Step: How to Bypass the Fuel Pump Relay

Step 1: Safety First

Disconnect the negative battery terminal to prevent accidental shorts or electrical damage. Work in a well-ventilated area, away from open flames or smoking materials. Gasoline fumes are flammable .

Step 2: Locate the Fuel Pump Relay

The fuel pump relay is usually in the under-hood fuse box, often labeled "FUEL PUMP" or "FP." In most Chevy trucks, the fuse box is near the battery or along the inner fender. If you can't find it, check your owner's manual or look for a rectangular relay with four or five pins. On some models, the relay is behind the headlight on the driver's side .

Step 3: Remove the Relay

Gently pull the relay out of its socket. You may need a relay puller tool or a small screwdriver. Do not force it, as you can damage the socket .

Step 4: Identify the Correct Terminals

Look at the diagram on the relay or the fuse box cover. The two terminals you need to connect are:

  • Pin 30 – Power source (battery voltage)
  • Pin 87 – Fuel pump power output

These are typically the two largest terminals on the relay socket. Do not jumper pins 85 and 86, as those are the relay coil control terminals and can cause damage if jumpered incorrectly .

Step 5: Insert the Jumper Wire

Take your jumper wire and connect pin 30 to pin 87 in the relay socket. This bypasses the relay and sends power directly from the battery to the fuel pump. Make sure the connection is secure and that the wire does not touch any other metal surfaces .

Step 6: Test the Fuel Pump

Turn the ignition key to the ON position (do not start the engine). You should hear the fuel pump running – a buzzing or whirring sound coming from the fuel tank area. If you hear it, the fuel pump is working and the relay is likely the problem. If you don't hear anything, the fuel pump itself may be faulty .

Step 7: Interpret the Results

  • Fuel pump runs when bypassed – The relay or its control circuit is bad. Replace the relay with a new one. If the problem continues, check the wiring and PCM signal .
  • Fuel pump does not run when bypassed – The fuel pump is likely dead, or there is a wiring issue between the relay socket and the pump. Check for corrosion, broken wires, or a bad ground connection .

Step 8: Remove the Jumper Wire and Reinstall the Relay

Once your test is done, turn off the ignition, remove the jumper wire, and put the relay back in its socket. Reconnect the negative battery terminal. Do not drive with the jumper wire in place, as it can overheat the fuel pump or drain the battery .

Alternative Method: Using a Copper Wire

If you don't have a jumper wire, you can use a 5-inch copper wire with about half an inch of insulation stripped off both ends. Push one end into the pin slot of the high left corner of the relay socket, and the other end into the pin slot at the bottom right. This creates a direct connection and works the same way as a jumper wire .

A Quick Test: Swap with Another Relay

Before jumping the relay, try this simple trick: find another relay in the fuse box with the same part number (like the horn relay or A/C relay). Swap it into the fuel pump relay socket. If the truck starts, you know the original relay was bad. This is a cleaner, safer diagnostic method than using a jumper wire .

Important Safety Warnings and Common Mistakes

  • Do not drive with the relay bypassed – This is a temporary test only. Running the fuel pump continuously can overheat it and cause damage .
  • Avoid wrong connections – Jumping the wrong terminals can short out the electrical system, blow fuses, or damage the PCM. Always double-check your wiring .
  • Use insulated tools – Metal tools can cause shorts. Wear rubber gloves if possible .
  • Watch for sparks – Gasoline fumes are highly flammable. Never work near open flames .

What to Do Next: Replace the Faulty Relay

If the test confirms the relay is bad, replace it with a new one. Relays are inexpensive and easy to find at auto parts stores. If the fuel pump itself is faulty, you will need to replace it. This is a more involved job that may require dropping the fuel tank or removing the bed on a pickup truck.

Upgrade Your Fuel System with KEMSO Fuel Pumps

If you find that your fuel pump needs replacement, consider upgrading to a KEMSO brand fuel pump. KEMSO fuel pumps are high-performance, OEM replacement parts designed to deliver reliable fuel delivery and long-lasting durability. Every KEMSO fuel pump comes with a lifetime warranty, giving you peace of mind on every drive. Whether you own a Chevy truck, a motorcycle, an ATV, or a personal watercraft, KEMSO offers a wide range of fuel pumps that meet or exceed factory specifications. Visit the KEMSO online store to find the perfect fuel pump for your vehicle and keep your engine running at its best.

Visit KEMSO Racing for more information: https://www.kemsoracing.com/

Final Thoughts

Bypassing the fuel pump relay on a Chevy truck is a straightforward diagnostic procedure that can save you time and money. It helps you quickly determine whether the relay or the fuel pump is the cause of your no-start problem. Remember, this is a temporary fix, not a permanent solution. Always replace the faulty relay or fuel pump as soon as possible to keep your truck safe and reliable on the road.

If you are unsure about any step, consult a professional mechanic. Working with electrical systems and fuel components requires caution, but with the right approach, you can get your Chevy truck back in action quickly.

For high-quality replacement fuel pumps with lifetime warranty, check out KEMSO at https://www.kemsoracing.com/.


Back to blog