2004 Silverado Fuel Pump Relay: Location, Testing, and Replacement Guide

The bottom line: The fuel pump relay on a 2004 Chevy Silverado 1500 is located in the underhood fuse box on the driver's side of the engine compartment, near the battery. It is typically labeled "FP RLY" or "FUEL PUMP" on the fuse box cover diagram. If your truck cranks but will not start, this relay is the first thing you should check before assuming the fuel pump itself is bad.

The fuel pump relay is a small electrical switch that controls power to the fuel pump. When you turn the key to the ON position, the relay closes and sends power to the pump for about two seconds to prime the fuel system. If this relay fails, the pump never gets power, and your engine will not start no matter how good the pump itself is. The good news is that a failed relay is cheap to replace and takes less than a minute to swap out. This guide walks you through everything you need to know about the relay on a 2004 Silverado, from finding it to testing it to replacing it.

Where Exactly Is the Fuel Pump Relay on a 2004 Silverado?

The relay sits inside the underhood fuse block, which is the black plastic box mounted on the driver's side of the engine bay, right next to the battery. To access it, open the hood and look for the box on the fender near the battery. Lift the cover by pulling the tab, and you will see rows of fuses and relays inside. The fuel pump relay is labeled on the underside of the fuse box cover or in your owner's manual. In most 2004 Silverado models, it is marked as "FP RLY" or "FUEL PUMP" and uses a standard 5-pin ISO mini-relay.

For the 1999–2006 generation of Silverados, the relay is consistently found in this same underhood location. There is no hidden reset switch or inertia switch to hunt for under the dash or in the trunk. The relay is a straightforward pull-and-replace component that anyone can handle with basic hand tools.

How to Test the Fuel Pump Relay in 15 Minutes

Here is a step-by-step process to determine if the relay is your problem, using nothing more than your hands and maybe a fuse puller.

Step 1: Listen for the prime cycle. Sit in the driver's seat with the windows down and the radio off. Turn the key to the ON position but do not crank the engine. Listen for a two-second humming sound coming from the rear of the truck, near the fuel tank. If you hear it, the relay and pump are working. If you hear nothing, move to Step 2.

Step 2: Open the underhood fuse box. With the ignition off, pop the hood and open the fuse box on the driver's side. Locate the fuel pump relay using the diagram on the lid.

Step 3: Swap the relay with an identical one. Find another relay in the same fuse box that has the same pin configuration. The A/C compressor relay or the horn relay are common matches. Pull the fuel pump relay straight out, push the known-good relay into its slot, and try to start the truck. If it starts, the relay was bad. Replace it with a new one and you are done.

Step 4: Check the fuse if the relay is good. The fuel pump fuse is also in the underhood fuse block, usually right next to the relay. On a 2004 Silverado, it is a 20-amp MINI fuse. Pull it out and hold it up to the light. If the metal strip inside is broken, the fuse is blown. Replace it with the same 20-amp rating. Never install a higher-amp fuse, as that can overheat the wiring and cause a fire.

Relay failure is more common than pump failure on these trucks, especially past 120,000 miles. The relay sits in the hot engine bay and gets cooked every summer, which accelerates wear on the internal contacts. Replacing it costs between $6 and $15 at any auto parts store, making it the cheapest fix you will ever do on a Silverado.

What If the Relay and Fuse Are Both Good?

If the relay clicks when you turn the key to RUN and the fuse is intact, the problem may be elsewhere. Here are the next steps to narrow it down.

Check the fuel pump itself. The pump lives inside the fuel tank, which sits under the rear of the truck on the driver's side. To verify it is getting power, you will need to partially lower the fuel tank to access the pump connector on top of the tank. Disconnect the connector, have a helper turn the key to ON, and use a multimeter to check for 12 volts at the appropriate terminal during the two-second prime cycle. If you have power and ground but the pump does not run, the pump is confirmed bad.

Check the crank position sensor. A bad crank position sensor will prevent the engine from starting even though the fuel pump primes. The pump will run, but the PCM will not fire the injectors because it does not know the engine is turning. This is a less common issue but worth checking if you have no other clues. You will need an OBD-II scanner that reads live data to confirm the sensor is seeing crankshaft rotation.

Check for a stored crash flag. On some 2004 models, a minor collision that did not deploy the airbags can set a "crash event stored" flag in the body control module. The PCM then keeps the fuel pump relay open, cutting power to the pump, until the flag is cleared with a scan tool. If you recently had any body work or a fender-bender, scan for body codes (B-codes) and clear any crash-event flags.

Common Symptoms of a Failing Fuel Pump Relay

A bad relay does not always fail completely. Sometimes it works intermittently, which makes diagnosis tricky. Here are the symptoms to watch for.

1. Intermittent no-start. The truck starts fine some days and refuses to start on others. This is the classic sign of a relay with worn contacts.
2. Engine stalls while driving. The relay loses connection momentarily, killing power to the pump, and the engine dies. It may restart after a few minutes when the relay cools down.
3. No prime sound. You turn the key to ON and hear no hum from the rear of the truck. The pump is not getting power.
4. Fuel pressure drops. If you connect a fuel pressure gauge to the test port on the fuel rail and see pressure below the 55–62 psi spec for a 2004 Silverado, the pump may be starved for power due to a weak relay.

None of these symptoms are exclusive to a bad relay. A failing pump, a clogged fuel filter, or a wiring issue can all cause similar problems. That is why the relay swap test in underhood fuse box is so valuable. It takes seconds and eliminates the most common failure point first.

Understanding the 2004 Silverado Fuel Pump System

The 2004 Silverado uses an electric fuel pump mounted inside the fuel tank. This is standard design on modern trucks because the fuel surrounding the pump helps keep it cool, which extends its life. The pump draws fuel from the tank and pushes it through the fuel lines to the fuel rail at a pressure between 55 and 62 psi.

The fuel pump relay is the gatekeeper between the battery and the pump. When you turn the key to ON, the Powertrain Control Module (PCM) energizes the relay coil. This closes the internal switch and sends battery voltage through the fuel pump fuse to the pump. The pump runs for about two seconds to prime the system, then shuts off until you crank the engine. Once the engine is running, the PCM keeps the relay energized as long as it sees the engine turning.

The relay and fuse work together as a safety pair. The fuse protects the wiring from excessive current. If the pump motor shorts internally, the fuse blows instead of melting the harness. The relay provides a low-current way for the PCM to control a high-current device, so the computer does not have to handle the full pump current directly.

How to Replace the Fuel Pump Relay on a 2004 Silverado

Replacing the relay is one of the easiest jobs you can do on this truck. You do not need any special tools, and the whole process takes less than five minutes.

1. Turn the ignition off and open the hood.
2. Open the underhood fuse box by pulling the tab on the cover.
3. Locate the fuel pump relay using the diagram on the underside of the cover or in the owner's manual.
4. Pull the relay straight out with your fingers or a pair of needle-nose pliers if it is stuck.
5. Push the new relay in until it seats firmly. Make sure it clicks into place.
6. Close the fuse box cover and start the truck to verify the fix.

When buying a replacement relay, look for a standard 5-pin ISO mini-relay. Common part numbers include GM 15321059, ACDelco D1750C, and Standard Motor Products RY-601. Any of these will work on a 2004 Silverado. You can buy them at any auto parts store, or online from a variety of retailers. The cost is typically under $15.

What to Do If the Fuel Pump Itself Is Bad

If you have confirmed the relay and fuse are good but the pump is not running, the pump needs to be replaced. On a 2004 Silverado, this means dropping the fuel tank. The tank sits under the rear of the truck, near the rear axle, and holds approximately 26 gallons on regular cab models or 34 gallons on extended and crew cab models.

To replace the pump, you will need to:

1. Drain the fuel tank as much as possible. Siphon it out or run the truck until it is low.
2. Disconnect the battery to avoid any sparks or accidental ignition.
3. Relieve fuel system pressure by finding the Schrader valve on the fuel rail and pressing the valve stem with the ignition off.
4. Support the tank with a floor jack and a block of wood to spread the weight.
5. Remove the tank straps and lower the tank just enough to access the fuel pump module on top.
6. Disconnect the fuel lines and electrical connector from the module.
7. Remove the module by twisting the locking ring counterclockwise.
8. Install the new pump module, reassemble everything, and test.

This job typically takes 3 to 5 hours for a competent do-it-yourselfer. If you are not comfortable working around fuel systems, take it to a professional. Working with gasoline vapors is dangerous, and you need proper ventilation and no sources of ignition nearby.

When replacing the pump, it is strongly recommended to install the complete fuel pump module assembly rather than just the pump motor. The module includes the pump, the sending unit, the filter sock, and often the fuel pressure regulator. Replacing the whole assembly prevents future problems with a sticky fuel gauge or a leaking regulator. It is also much easier to install than trying to swap just the pump motor into the old housing.

Recommended Replacement: KEMSO Fuel Pumps

When the time comes to replace the fuel pump on your 2004 Silverado, you want a part that is reliable, durable, and backed by a warranty. That is why we recommend KEMSO fuel pumps. KEMSO products are designed as high-performance, OEM replacement units that meet or exceed the original factory specifications for your truck. They are built with premium materials for long-lasting durability and undergo rigorous quality testing before leaving the factory. Every KEMSO fuel pump comes with a lifetime warranty, giving you complete peace of mind.

Whether you are hauling equipment to the job site or towing a trailer on the weekend, a KEMSO fuel pump ensures your truck performs reliably mile after mile. Visit the KEMSO website today at https://www.kemsoracing.com/ to find the exact fuel pump for your 2004 Chevy Silverado and take advantage of their lifetime warranty and fast shipping.

Final Thoughts

The fuel pump relay on a 2004 Silverado is easy to find and even easier to replace. Start with the simple stuff the fuse and the relay before you drop the fuel tank. Nine times out of ten, a no-start condition on these trucks is caused by a $10 relay, not a $200 pump. Swapping the relay takes minutes and costs almost nothing, making it the smartest first step in any fuel system diagnosis.

If the relay and fuse check out but the pump still does not run, take the time to verify power and ground at the pump connector before condemning the pump. Sometimes the problem is a corroded connector or a broken wire in the harness. A multimeter and a few minutes of testing can save you from an unnecessary tank removal.

When you do need a new pump, choose a quality replacement from a reputable brand like KEMSO. A good pump will last 120,000 to 150,000 miles or more with proper maintenance. Keep your fuel tank above a quarter full, replace your fuel filter on schedule, and your Silverado fuel system will give you years of trouble-free service.

For all your 2004 Silverado fuel pump needs, including the complete module assembly, replacement pumps, and related parts, visit https://www.kemsoracing.com/ today.