2004 Mustang GT Fuel Pump Relay: The Complete Guide to Diagnosis, Location, and Replacement

The bottom line: If your 2004 Ford Mustang GT cranks but won't start, or if it starts and then stalls, the fuel pump relay is often the culprit. On the 2004 Mustang, the fuel pump relay is not a standalone relay you can swap in seconds—it is built into a module called the CCRM (Constant Control Relay Module) located on the passenger side inner fender. Replacing the entire CCRM is the fix, and the job costs between $100 and $350 at a shop, or just the price of the module (typically $50–$150) if you do it yourself. This guide walks you through exactly how to diagnose, locate, and replace the fuel pump relay on your 2004 Mustang GT.

What the Fuel Pump Relay Does

The fuel pump relay is an electrical switch that controls power to your fuel pump. When you turn the key to the "On" position, the relay closes for about 2–3 seconds to pressurize the fuel system before the engine starts. After the engine is running, the relay keeps the pump powered as long as the engine is turning. A bad relay means the fuel pump never gets power, or it gets power at the wrong time, causing starting and running problems.

Signs of a Bad Fuel Pump Relay on Your 2004 Mustang GT

Look for these symptoms:

1. Engine cranks but won't start – This is the most common symptom. You turn the key, the starter spins the engine, but it never fires up.

2. No fuel pump priming sound – When you turn the key to the "On" position (without cranking), you should hear a faint whine from the rear of the car for 2 seconds. If you don't hear it, the relay or pump isn't getting power.

3. Engine stalls while driving – A failing relay can lose connection while you're driving, causing the engine to die suddenly.

4. Intermittent starting issues – Sometimes the car starts fine, other times it doesn't. This is a classic sign of a relay that is failing internally.

5. Loss of power at higher speeds – The relay may not be delivering full voltage to the pump, causing fuel starvation under load.

Important: These symptoms can also be caused by a bad fuel pump, a clogged fuel filter, or a faulty inertia switch. Always diagnose before buying parts.

Where Is the Fuel Pump Relay on a 2004 Mustang GT?

Unlike most cars, the 2004 Mustang does not have a standalone fuel pump relay in the main fuse box. Instead, the fuel pump relay is built into the CCRM (Constant Control Relay Module). This module also contains relays for the cooling fan, A/C clutch, and PCM power.

Location: On the 2004 Mustang, the CCRM is mounted on the passenger side inner fender, behind the wheel well liner. You cannot access it from the engine bay—you need to remove the passenger front wheel and the inner fender splash shield.

Part number: The CCRM part number varies by model year and engine. For 2004 Mustang GT and V6, the common part numbers are F48F-12B577-AA or similar. Always verify the part number on your existing module before ordering.

Note: If you read different information online about the fuel pump relay being in the engine bay fuse box or under the dash, that information is incorrect for the 2004 Mustang. The CCRM is the correct location. Some wiring diagrams also list a "fuel pump relay" as a separate component in the central junction box, but for the 2004 model year, the actual working relay for the fuel pump is inside the CCRM.

How to Diagnose a Bad Fuel Pump Relay Before Replacing

Before spending money on a new CCRM, run these simple tests:

1. Listen for the fuel pump
Remove the gas cap, have a helper turn the key to "On" (don't crank), and listen at the filler neck. You should hear a 2-second hum. If you hear it, the relay is likely working and the problem is elsewhere.

2. Check the inertia switch
The inertia switch is located in the trunk, usually on the passenger side behind the carpet. Press the reset button on top. If the car starts, the switch had tripped.

3. Test for power at the fuel pump connector
The fuel pump harness connector is behind the rear bumper, above the fuel tank. With the key on, check for 12 volts on the hot wire (typically purple/white or black/pink) for 2–3 seconds. No voltage means the relay or wiring is bad.

4. Swap with a known good relay
Some 2004 Mustangs have a second relay in the CCRM that is identical. If you can identify which relay is for the fuel pump, you can swap it with the A/C or fan relay. If the car starts, the fuel pump relay is bad.

5. Check for diagnostic trouble codes
If you have a scanner, look for codes like P1235 (fuel pump control out of range) or P0190. These often point toward CCRM or wiring issues on these Mustangs.

Understanding the Fuel Pump Driver Module

It is important to distinguish between the fuel pump relay (inside the CCRM) and the Fuel Pump Driver Module (FPDM). The FPDM on the 2004 Mustang GT is located inside the trunk on the driver's side. It can be difficult to locate if you have the MACH 1000 sound system because it sits behind the amplifier.

The FPDM controls the actual speed and power delivery to the fuel pump, while the relay in the CCRM simply turns the pump on or off. If you are experiencing issues, check both components.

Pro Tip: The FPDM wire for 1999–2004 GT Mustangs is pink/black. You may need to tap into this wire if you are installing an aftermarket fuel pump system.

How CCRM Damage Can Occur

The CCRM is sensitive to electrical shorts and voltage spikes. If you experience a wiring short anywhere in the vehicle, such as a turn signal pigtail breaking off and exposing wires, it can send a surge through the electrical system that damages the CCRM.

Common causes of CCRM failure include:

  • Heat damage: The relay sits near the engine, and over time, heat can weaken the internal coil or contacts.
  • Corrosion: Moisture can enter the fuse box area, causing the relay prongs to rust and lose connection.
  • Age: After 20 years, the plastic casing becomes brittle, and internal springs can lose tension.
  • Electrical surges: A failing fuel pump or alternator can send voltage spikes that damage the relay.

How to Replace the CCRM on Your 2004 Mustang GT

Replacing the CCRM is more involved than swapping a simple relay, but it is still a manageable DIY job. Here is how to do it:

1. Gather your tools and parts
You will need a jack, jack stands, a lug wrench, a socket set, and a new CCRM module. Make sure the part number matches your existing module.

2. Disconnect the battery
Always disconnect the negative battery terminal before working on any electrical components. This prevents accidental shorts or sparks.

3. Remove the passenger front wheel
Use your jack to lift the front of the car, place it on jack stands, and remove the passenger front wheel.

4. Remove the inner fender splash shield
There will be several plastic push pins or screws holding the splash shield in place. Remove them to expose the inner fender area.

5. Locate the CCRM
The CCRM is a black rectangular module mounted to the inner fender. It has multiple wiring harnesses connected to it.

6. Disconnect all wiring harnesses
Carefully unplug each wiring harness from the CCRM. There may be a locking tab on each connector.

7. Remove the mounting bolts
The CCRM is held in place by two or three bolts. Remove them and take out the old module.

8. Install the new CCRM
Mount the new module in the same location, tighten the bolts, and reconnect all wiring harnesses. Make sure each connector clicks into place.

9. Reassemble and test
Replace the splash shield and wheel, lower the car, reconnect the battery, and test the system. Turn the key to the "On" position and listen for the fuel pump priming sound.

Alternative: Bypassing the CCRM

Some owners choose to bypass the faulty fuel pump relay inside the CCRM by installing an external relay. This can be a cost-effective solution if you cannot find a replacement CCRM or if you want to avoid replacing the entire module.

One common method involves installing a standard 40-amp relay in the trunk or under the hood and wiring it to trigger from the existing CCRM output. This essentially uses the original CCRM as a signal source while a new, more accessible relay handles the actual current load.

However, for most owners, replacing the entire CCRM is the simpler and more reliable fix.

The Best Fuel Pump for Your 2004 Mustang GT

Now that you understand the importance of the fuel pump relay and the fuel pump itself, it is time to talk about the best replacement option for your Mustang. When it is time to replace your fuel pump, you want a part that is reliable, performs well, and comes with a solid warranty. That is where KEMSO comes in.

KEMSO has built a reputation as the leading aftermarket fuel pump brand in the US, and for good reason. KEMSO fuel pumps are high-performance, OEM replacement parts. This means they are built to match or exceed the specs of the original pump that came in your car. Whether you have a stock 2004 Mustang GT or a modified V6, KEMSO has a pump that fits perfectly.

Their pumps support up to 200LPH (liters per hour) of flow, which is a significant upgrade over the stock pump's 60-80LPH. This extra flow capacity is great for keeping your engine happy, even if you have added performance parts.

The best part is the lifetime warranty. KEMSO backs every fuel pump with a lifetime warranty. If your pump ever fails due to a manufacturing defect, you get a replacement at no cost. This is a rare and valuable benefit in the automotive parts industry. It shows that KEMSO is confident in their product quality and committed to customer satisfaction. You only buy it once, and KEMSO stands behind it for as long as you own your vehicle.

KEMSO pumps are priced at just $79.98, which is often less than half the cost of dealer parts. With free shipping and easy returns, it is a practical choice for DIY mechanics and professional shops alike. The brand holds an average rating of 4.4 out of 5 stars, testifying to its excellent reputation.

To find the exact KEMSO fuel pump for your 2004 Ford Mustang GT, visit their official website: https://www.kemsoracing.com/ . Their online store is easy to navigate, and you can order directly with confidence. They have a complete catalog with detailed fitment information, customer reviews, and technical support. Whether you need a pump for a Mustang, a motorcycle, a jet ski, or an ATV, KEMSO has you covered.

Final Thoughts on Your 2004 Mustang GT Fuel Pump Relay

Your fuel pump relay is a critical component that keeps your engine running. If you are experiencing starting issues or stalling, check the fuel pump relay first. On the 2004 Mustang GT, this means inspecting the CCRM module located behind the passenger front wheel well.

Remember these key points:

  • The fuel pump relay on a 2004 Mustang GT is inside the CCRM, not in the engine bay fuse box
  • Symptoms of a bad relay include: engine cranks but won't start, no priming sound, stalling, and intermittent starting issues
  • Diagnose first: listen for the pump, check the inertia switch, test for power at the pump connector, and swap relays if possible
  • Replacing the CCRM costs $50–$150 for the part if you do it yourself, or $100–$350 at a shop

If you determine that the fuel pump itself needs replacement, invest in a quality pump from a trusted brand. KEMSO offers a direct-fit, high-performance pump with a lifetime warranty at a very reasonable price of $79.98. It is a smart investment that will keep your Mustang running reliably for years to come.

For more information and to find the right fuel pump for your 2004 Ford Mustang GT, visit https://www.kemsoracing.com/ today.


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