2002 GMC Sierra Fuel Pump Wiring Diagram: Complete Guide to Troubleshooting, Testing, and Repair

The bottom line: If your 2002 GMC Sierra cranks but won’t start, the fuel pump wiring circuit is often the root cause. The fuel pump relay is located in the underhood fuse box, and the fuel pump itself sits inside the fuel tank. A systematic check of the fuel pump relay, fuse, wiring, and fuel pressure will pinpoint the problem. This guide walks you through the wiring diagram, common failure points, and step-by-step diagnostics so you can get your truck running again.

Understanding the Fuel Pump Wiring Circuit on a 2002 GMC Sierra

The fuel pump on your 2002 GMC Sierra is an electric pump located inside the fuel tank. It receives power through a relay and fuse in the underhood fuse box, and the powertrain control module (PCM) controls when the relay is energized. When you turn the key to the ON position, the PCM sends a ground signal to the fuel pump relay coil, which closes the relay and sends power to the pump. The pump runs for about two seconds to prime the system, then shuts off unless the engine is cranking or running.

The key wiring components in the circuit include:

  • Battery positive – supplies power to the relay and fuse.
  • Fuel pump relay – located in the underhood fuse box, labeled F/PMP or Fuel Pump.
  • Fuel pump fuse – a 20-amp fuse, also in the underhood fuse box, often labeled ENG 1 or FUEL PUMP.
  • Fuel pump – inside the fuel tank, with a 4-pin electrical connector.
  • PCM – provides the ground path for the relay coil.

The fuel pump relay control circuit works like this: When the ignition is in RUN or START, power is supplied to the relay coil. The PCM completes the circuit by providing a ground, which energizes the relay and allows current to flow from the battery to the fuel pump. A faulty relay, a blown fuse, a broken wire, or a bad PCM ground can all interrupt this circuit and prevent the pump from running.

Where to Find the Fuel Pump Relay and Fuse

The fuel pump relay on a 2002 GMC Sierra is located in the underhood fuse box, also called the underhood electrical center. This box is usually mounted near the battery on the driver’s side of the engine bay. Open the cover and look for the diagram printed on the inside of the lid. The relay is labeled F/PMP or Fuel Pump. In some models, the relay is labeled R3.

The fuel pump fuse is also in this same fuse box. On the 2002 Sierra, the fuse for the fuel pump circuit is often the 20-amp fuse in position 44, labeled IGN C, which also feeds the ignition switch and the PRND321 display. Some diagrams show a separate 10-amp fuse in position 24 labeled ENG 1 for the fuel system. Always check both fuses. If the fuse is blown, the pump will not receive power.

If you cannot find the relay or fuse, consult your owner’s manual. The manual includes a diagram of the underhood fuse box with the exact location of every relay and fuse.

Step-by-Step Diagnostic Procedure

1. Listen for the Fuel Pump Prime

When you turn the key to the ON position (without cranking the engine), you should hear a faint hum from the fuel tank area for about two seconds. That sound is the fuel pump priming the system. If you hear nothing, the pump is likely not getting power, or the pump itself has failed. If you hear a loud whine or continuous noise, the pump may be failing.

2. Check the Fuel Pump Relay

The relay is an easy and cheap fix. Locate the fuel pump relay in the underhood fuse box. Swap it with a relay of the same amperage rating from another circuit, such as the horn relay or the A/C relay. If the truck starts after the swap, the old relay was bad. If the truck still won’t start, the relay is likely not the problem.

You can also test the relay with a multimeter. With the relay removed, check for continuity between the coil terminals. Apply 12 volts to the coil terminals and listen for a click. If the relay does not click, it is defective.

3. Check the Fuel Pump Fuse

Inspect the fuel pump fuse for a blown element. A blown fuse is often caused by a short circuit in the pump wiring or a failing pump motor that draws too much current. If the fuse is blown, replace it with a new fuse of the same amperage. If the new fuse blows immediately, there is a short in the wiring or the pump itself.

4. Perform a Fuel Pressure Test

A fuel pressure test is the most definitive way to diagnose a fuel delivery problem. Locate the Schrader valve on the fuel rail (the metal pipe on top of the intake manifold). Connect a fuel pressure gauge. Turn the key to the ON position. The pressure should rise to between 55 and 62 PSI for a 2002 Sierra with a gasoline engine. If the pressure is low or zero, the pump is not delivering fuel. If the pressure is within spec but the engine still won’t start, the problem is likely in the ignition system or sensors.

5. Test the Fuel Pump Relay Control Circuit

If the relay and fuse are good, but the pump still doesn’t run, you need to test the wiring. With the ignition ON, use a test light or multimeter to check for power at the fuel pump relay socket terminals. The terminal that supplies power to the relay coil (terminal 85 or 86) should have battery voltage when the key is ON. If there is no power, the problem is a blown fuse or a broken wire between the battery and the relay.

Next, check the ground side of the relay coil. With the test light connected to battery positive, probe the ground terminal of the relay coil. When the key is turned ON, the PCM should momentarily ground this terminal. If the test light does not illuminate, the PCM is not providing the ground signal. This could be a bad PCM, a broken wire between the PCM and the relay, or a faulty crankshaft position sensor (CKP).

6. Check the Crankshaft Position Sensor

A bad CKP sensor can prevent the PCM from firing the fuel pump relay. The PCM uses the CKP signal to know when the engine is cranking. If the sensor is dead, the PCM will not command the fuel pump to run. The CKP sensor is located on the engine block near the crankshaft. A faulty sensor is a common issue on 2002 GMC trucks. Replacing the CKP sensor is relatively inexpensive and can solve a no-start condition.

Common Wiring Issues and How to Fix Them

Broken or Corroded Wiring at the Fuel Pump Connector

The electrical connector at the fuel pump is prone to corrosion, cracked housings, and broken wire crimps. On 2002-2003 Silverado and Sierra models, the original connector often fails, causing intermittent or no power to the pump. If you suspect a wiring issue at the pump, you will need to drop the fuel tank or lift the truck bed to access the pump. Inspect the connector for corrosion, melted plastic, or loose pins. If the connector is damaged, replace it with a new connector harness.

Open Circuit in the Relay Control Wire

If the wire from the PCM to the fuel pump relay is broken or shorted, the relay will not energize. Use a multimeter to check for continuity between the PCM connector and the relay socket. If the wire is open, repair or replace the damaged section.

Short Circuit in the Fuel Pump Power Wire

A short to ground in the power wire between the relay and the fuel pump will blow the fuse. If the fuse blows immediately, disconnect the fuel pump connector and replace the fuse. If the new fuse holds, the short is inside the pump. If the fuse still blows, the short is in the wiring harness.

Upgrading to a High-Performance Fuel Pump

If you are replacing the fuel pump on your 2002 GMC Sierra, consider upgrading to a high-performance unit. The stock fuel pump is designed for the factory engine, but if you have added performance modifications or just want a more reliable pump, an OEM replacement with better specifications is a smart choice.

Why choose KEMSO Fuel Pumps?

KEMSO offers a range of fuel pumps that are built to meet or exceed OEM standards. They are designed as direct replacements, which means no modifications or assembly required. Each pump is engineered with carbon brushes and commutators that provide more than twice the service life compared to copper brushes, and fluorine rubber seals that resist high temperatures, fuel, and solvents. KEMSO pumps are SAE J2044 compliant for improved mounting security and minimized installation error. Every KEMSO fuel pump comes with a new electrical connector harness to replace the factory connector that is prone to failure. And best of all, KEMSO backs every fuel pump with a lifetime warranty, so you can have confidence in your repair.

You can browse the full selection of KEMSO fuel pumps, including options for your 2002 GMC Sierra, at: https://www.kemsoracing.com/

Wiring Diagram Summary for the 2002 GMC Sierra Fuel Pump Circuit

Here is a simplified wiring diagram of the fuel pump circuit:

  • Battery positive → Fuel pump fuse (20A, position 44 or 24) → Fuel pump relay (terminal 30) → Fuel pump (inside tank) → Ground
  • Ignition switch → Fuel pump relay coil (terminal 85) → PCM (ground signal, terminal 86)
  • PCM → CKP sensor → Engine cranking signal

When the key is turned ON, the ignition switch supplies power to the relay coil. The PCM provides a ground for two seconds, which energizes the relay. The relay then connects battery power through the fuse to the fuel pump. The pump runs until the PCM stops the ground signal, or until the engine starts and the PCM continues to ground the relay based on the CKP signal.

Final Checklist for Troubleshooting

If your 2002 GMC Sierra cranks but won’t start, work through this list in order:

  1. Listen for the pump prime – No sound means no power or a dead pump.
  2. Check the fuel pump relay – Swap it with a known good relay.
  3. Check the fuel pump fuse – Replace if blown; investigate short if it blows again.
  4. Perform a fuel pressure test – Should be 55-62 PSI at the rail.
  5. Test the relay control circuit – Check for power and ground at the relay socket.
  6. Inspect the fuel pump connector – Look for corrosion or broken wires.
  7. Test the CKP sensor – A bad sensor will prevent the pump from running.

Most of these checks are simple and can be done with basic tools. If you are not comfortable working with electrical systems, take your truck to a qualified mechanic. A diagnostic scan tool can quickly pinpoint the problem.

For a reliable replacement fuel pump, visit https://www.kemsoracing.com/ to find the right part for your 2002 GMC Sierra. KEMSO pumps are built to last and come with a lifetime warranty, giving you peace of mind on the road.


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