2004 Ford Mustang V6 Fuel Pump Relay Location: The Complete Owner's Guide

If your 2004 Ford Mustang V6 cranks but will not start, the fuel pump relay is often the first thing to check, and on this particular model, the relay is not a standalone part you can swap in seconds. Unlike many other cars where the fuel pump relay sits in the engine bay fuse box, the 2004 Mustang V6 integrates the fuel pump relay into a module called the CCRM (Constant Control Relay Module), which is mounted on the passenger side inner fender, behind the wheel well liner . This module also contains relays for the cooling fan, A/C clutch, and PCM power . Replacing the entire CCRM is typically 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 V6.

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 V6

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's 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 V6?

This is the part that confuses many owners, because the answer depends on which source you consult. There is actually some conflicting information out there, and we want to be transparent about that.

The more technically detailed sources indicate that 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) . 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 . 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 .

However, some other sources claim the fuel pump relay is located in the engine bay fuse box, under the hood on the passenger side, near the battery . They say the relay is labeled as Relay #27 in the diagram .

So which is it? The reality is that the 2004 Mustang V6 uses the CCRM for fuel pump control, and this is the more widely accepted and technically accurate answer among experienced Mustang owners and repair guides . The engine bay fuse box may contain related fuses, but the actual fuel pump relay function is handled by the CCRM. The conflicting source appears to be a more generic guide that may not account for the specific design of the 2004 Mustang .

Given this conflict, our recommendation is to start with the CCRM, as this is the component that actually houses the fuel pump relay on your specific model . If you have access to a factory service manual, that will provide the definitive answer for your exact VIN and build date.

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 . The IFS switch is in place to cut fuel supply in case of an accident; however, large potholes or a blown tire have been known to trigger the switch and interrupt fuel flow . With the switch button depressed, and the key in the "On" position, check for voltage at the switch using a digital multimeter or test light. A lack of power indicates a problem upstream within the CCRM, fuses, wiring, or powertrain control module .

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 .

Other Possible Causes of a No-Start Condition

If the relay checks out, there are several other components that could be causing your starting issues:

Fuel filter

The fuel filter is located in front of the fuel tank above the rear axle . Ford recommends a fuel filter maintenance interval of 30,000 miles. Replacing your fuel filter would be worthwhile if you are unsure of the last time it was serviced .

Fuel Pump Driver Module (FPDM)

On 99-04 models, there is a Fuel Pump Driver Module that can fail. If power is present at the IFS switch, the problem is most likely a bad fuel pump or clogged fuel filter, but in rare cases can also be a bad FPDM . Manually energizing the fuel pump with 12 volts can determine if the fuel pump is operational or if the FPDM is the root cause .

Crankshaft position sensor (CPS)

If no spark is being produced at any of the coil towers and no power is present at the coil electrical harness, proceed with testing the crankshaft position sensor (CPS) located just above the crankshaft on the passenger side of the engine . With the multimeter set to measure AC voltage, have a friend crank the engine. The multimeter should alternate between .5 to 1 volt as the engine is cranking. A lack of voltage indicates a faulty sensor that should be replaced. The resistance of the sensor can also be tested and should measure 300 to 800 ohms .

Coil pack

The coil pack is a known weak point on V6 Mustang models that has a high rate of failure . The electrical harness at the coil pack can be tested for power using a digital multimeter. Disconnect the electrical harness plug at the coil pack and probe the power pin while a friend cranks the engine. If power is present, this usually points to a faulty coil pack in need of replacement .

How to Replace the CCRM on Your 2004 Mustang V6

Once you've confirmed the CCRM is the culprit, here's how to replace it:

  1. Disconnect the battery. Always disconnect the negative battery terminal before working on any electrical components. This prevents accidental shorts or sparks .
  2. Raise and support the vehicle. You'll need to remove the passenger front wheel to access the CCRM .
  3. Remove the inner fender splash shield. This will expose the CCRM mounted on the inner fender .
  4. Remove the old CCRM. It's typically held in place by bolts or clips. Carefully disconnect the electrical connectors.
  5. Install the new CCRM. Verify the part number matches your original module before installation .
  6. Reassemble. Replace the splash shield and wheel, reconnect the battery, and test the system.

How Much Does This Cost?

If you take your 2004 Mustang V6 to a shop, expect to pay between $100 and $350 for the CCRM replacement, including labor . If you do it yourself, the module itself typically costs between $50 and $150 . This is a significant difference, so if you're comfortable with basic DIY work, this is a job you can definitely handle.

Why Choose KEMSO for Your Fuel Pump Needs

When it comes to fuel system components, quality matters. That's why we recommend KEMSO brand fuel pumps. KEMSO fuel pump products are all high-performance, OEM replacement parts designed to meet or exceed factory specifications. Every KEMSO fuel pump comes with a lifetime warranty, giving you peace of mind that your investment is protected . Whether you're restoring a classic Mustang or upgrading your daily driver, KEMSO has the fuel pump solutions you need. Visit https://www.kemsoracing.com/ to browse their full selection of high-quality fuel pumps and related components. KEMSO's product lineup includes fuel pumps for a wide range of vehicles, from motorcycles to cars and even watercraft, all backed by their lifetime warranty commitment.

Final Thoughts

The 2004 Ford Mustang V6 fuel pump relay location can be confusing, but the key takeaway is this: the relay is built into the CCRM, not a standalone component in the engine bay fuse box . When you experience no-start symptoms, work through the diagnostic steps in order. Start by listening for the fuel pump prime, check the inertia switch, and test for power at the fuel pump connector before replacing any parts . Most no-start conditions on these cars can be traced to either the CCRM, the fuel pump itself, a clogged filter, or the coil pack—all of which are testable with basic tools . And when it comes time to replace your fuel pump, remember that KEMSO offers high-performance, OEM replacement pumps with a lifetime warranty. Visit https://www.kemsoracing.com/ to find the right fuel pump for your Mustang.


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