2004 Mustang Fuel Pump Fuse: Location, Diagnosis, and Complete Troubleshooting Guide

If your 2004 Ford Mustang GT or V6 is cranking but won't start, the first thing you should check is the fuel pump fuse. The fuel pump fuse on a 2004 Mustang is located in the engine compartment fuse box (also called the power distribution box). It is a 20-amp yellow mini fuse, labeled as fuse #14 . But here is what most owners don't realize: even if that fuse is good, the fuel pump relay is built into a module called the CCRM (Constant Control Relay Module), which is a common failure point on these cars . A blown fuse can cause the exact same symptoms as a bad pump or relay, and diagnosing it correctly will save you time and money.

The Bottom Line

The 2004 Mustang fuel pump system has three main electrical components you need to understand: the 20-amp fuse in the engine bay, the fuel pump relay inside the CCRM module, and the fuel pump itself. If your car won't start, start by checking fuse #14 in the engine compartment fuse box. If that fuse is good, the next suspect is the CCRM module, not the pump. Many owners replace the fuel pump multiple times before realizing the real issue was a bad relay inside the CCRM .

Understanding the 2004 Mustang Fuel Pump Electrical System

The fuel pump on a 2004 Mustang does not have a simple standalone relay that you can swap out in 30 seconds. Instead, Ford integrated the fuel pump relay into the Constant Control Relay Module (CCRM). This module also controls the cooling fan, A/C clutch, and PCM power relay .

Location of the CCRM Module

The CCRM is mounted on the passenger side inner fender, behind the wheel well liner. You cannot access it from the engine bay. To get to it, you need to remove the passenger front wheel and the inner fender splash shield. The part numbers for the CCRM on 2004 Mustang GT and V6 models are typically F48F-12B577-AA or similar .

Step 1: Check the Fuel Pump Fuse First

Before you start replacing expensive parts, check the fuel pump fuse. It takes less than two minutes and costs nothing.

Where to Find It

The fuel pump fuse is located in the engine compartment fuse box (power distribution box). On a 2004 Mustang, this box is on the driver's side of the engine bay, near the battery. Fuse #14 is a 20-amp yellow mini fuse .

How to Test It

  1. Open the engine compartment fuse box lid.
  2. Locate fuse #14. It should be labeled on the fuse box diagram.
  3. Pull the fuse out using a fuse puller or needle-nose pliers.
  4. Look at the metal element inside the fuse. If it is broken or melted, the fuse is blown.
  5. You can also test it with a multimeter set to continuity mode.

If the fuse is blown, replace it with another 20-amp yellow mini fuse. If it blows again immediately, you have a short circuit somewhere in the fuel pump wiring.

Important Note

According to the fuse box diagram for the 2004 Mustang, fuse #14 is specifically rated for the fuel pump . There is also a 30-amp fuse (#26) for the PCM, which can also cause no-start conditions if blown.

Step 2: What To Do If the Fuse Is Good

If the fuel pump fuse is intact but your car still won't start, the problem is likely not the fuse itself. Here is what to check next.

Listen for the Fuel Pump

Turn the key to the "ON" position without cranking the engine. You should hear a faint whining sound from the rear of the car for about 2 seconds. This is the fuel pump priming the system. If you don't hear it, the pump is not getting power .

Check the Inertia Switch

The inertia fuel shutoff switch is located in the trunk, usually on the passenger side behind the carpet. It is a safety device that cuts power to the fuel pump in a collision. Sometimes it can trip for no reason. Press the reset button on top. If the car starts afterward, the switch had tripped .

Test for Power at the Fuel Pump Connector

You can test for 12 volts at the fuel pump harness connector. This connector is located behind the rear bumper, above the fuel tank. With the key in the "ON" position, check the hot wire (typically purple/white or black/pink) for 12 volts. The voltage should only be present for 2-3 seconds during the prime cycle. If there is no voltage, the problem is upstream: either the relay, wiring, or the CCRM .

Step 3: Diagnosing the CCRM (Constant Control Relay Module)

If you have confirmed that the fuse is good and there is no power at the fuel pump connector, the CCRM is the most likely culprit. This is a very common failure point on 1998-2004 Mustangs .

Symptoms of a Bad CCRM

  • Engine cranks but does not start
  • No fuel pump priming sound
  • Intermittent starting issues (car starts fine one day, not the next)
  • Engine stalls while driving
  • Loss of power at higher speeds

How to Test the CCRM

You can perform a simple test to confirm the CCRM is bad. Since the CCRM contains multiple relays, you can try swapping the fuel pump relay with a known good relay inside the same module, such as the A/C or fan relay. If the car starts after the swap, the fuel pump relay inside the CCRM is bad .

How to Replace the CCRM

  1. Remove the passenger front wheel.
  2. Remove the inner fender splash shield.
  3. Locate the CCRM mounted on the inner fender.
  4. Disconnect the electrical connectors.
  5. Unbolt the module and replace it with a new one.
  6. Make sure to verify the part number matches your existing module.

The cost of a replacement CCRM is typically between $50 and $150 if you do it yourself. A shop will charge between $100 and $350 for the job .

Step 4: When the Fuel Pump Itself Is the Problem

Sometimes the fuel pump really is bad. On a 2004 Mustang, the fuel pump is located inside the fuel tank. Replacing it requires dropping the fuel tank, which is a significant job.

Signs of a Failing Fuel Pump

  • Whining noise from the fuel tank
  • Sputtering at high speeds
  • Loss of power under load
  • Car starts but runs rough
  • Fuel pump sounds weaker than it used to

How to Confirm the Pump Is Bad

The best way to confirm a bad fuel pump is to test fuel pressure. A 2004 Mustang should have around 30-45 psi at the fuel rail. If the pressure is low or nonexistent, and you have confirmed power at the pump connector, the pump itself is likely bad.

Checking Voltage at the Pump

If you measure 12 volts at the fuel pump connector during the prime cycle but the pump does not run, the pump is bad. If there is no voltage, the problem is in the relay or wiring .

Step 5: Common Wiring Issues and Short Circuits

On 2004 Mustangs, wiring issues can cause fuel pump problems. One common scenario is a short circuit in the turn signal or tail light wiring that can damage the CCRM or blow the fuel pump fuse .

What to Look For

  • Exposed wires from a broken turn signal pigtail
  • Melted or damaged wiring near the tail lights
  • Corroded connectors at the fuel pump or inertia switch

If you have recently had an electrical issue like a shorted turn signal, the wiring damage could have taken out the CCRM or the fuel pump relay. Check all wiring in the rear of the car carefully.

Ground Locations

Bad grounds are another common cause of fuel pump issues. The main ground points for the fuel system are:

  • G103 (right front of engine compartment)
  • G104 (left front of engine compartment)
  • G400 (left front of luggage compartment)

Make sure these grounds are clean, tight, and free of rust .

Step 6: Detailed Fuse Box Information for 2004 Mustang

Knowing the complete fuse box layout can help you diagnose other issues that might be related to the fuel pump.

Passenger Compartment Fuse Box

This fuse box is located under the instrument panel on the driver's side. Important fuses include:

  • Fuse #34 (20A): Instrument Cluster, CCRM, Data Link Connector, Securilock Transceiver Module
  • Fuse #35 (15A): Shift Lock Actuator, PCM, Speed Control Servo, ABS Module

If fuse #34 is blown, your CCRM may not function properly, which can affect the fuel pump relay .

Engine Compartment Fuse Box

In addition to fuse #14 for the fuel pump, here are other important fuses:

  • Fuse #6 (40A): Instrument Cluster, PCM
  • Fuse #26 (30A): PCM
  • Fuse #20: Generator (Alternator)

If the PCM loses power, the car will not start even if the fuel pump is good .

Step 7: Aftermarket Fuel Pump Upgrades

If you are replacing your fuel pump, you might consider upgrading to a higher-flow pump, especially if you have modified your engine. Many 2004 Mustang owners upgrade to aftermarket pumps for better performance.

What to Look For

  • High flow rate: Look for pumps rated at 340 LPH or higher for modified engines
  • Direct fit: Some aftermarket pumps are direct replacements that fit into the stock fuel hat
  • Warranty: A good warranty protects your investment

FPDM Wiring for Upgrades

If you are installing an upgraded fuel pump, you need to know the FPDM wire color. On 1999-2004 GT, Mach 1, and Cobra models, the FPDM wire is pink/black. This wire is used to trigger aftermarket relays or pump controllers .

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Summary: The 2004 Mustang Fuel Pump Fuse Troubleshooting Checklist

Here is a step-by-step checklist to diagnose your fuel pump issue:

  1. Check fuse #14 in the engine compartment fuse box. Replace if blown. If it blows again, look for a short circuit.
  2. Listen for fuel pump prime with key in ON position.
  3. Check the inertia switch in the trunk. Press the reset button.
  4. Test for 12 volts at the fuel pump connector (behind rear bumper, near fuel tank).
  5. If no power at pump, suspect the CCRM module. Attempt to swap relays inside the CCRM or replace the entire module.
  6. If power is present but pump doesn't run, replace the fuel pump.
  7. Check wiring and grounds for damage, especially if you recently had an electrical short.

Final Thoughts

The 2004 Mustang fuel pump fuse is just the starting point for diagnosing a no-start condition. While a blown fuse is an easy fix, the real culprit is often the CCRM module with its integrated fuel pump relay. By following the logical diagnostic steps outlined in this guide, you can avoid the common mistake of replacing the fuel pump multiple times only to find out the real problem was a $100 module.

Remember: always test before you replace. A multimeter and a few minutes of testing can save you hundreds of dollars and hours of labor. And when you do need a replacement fuel pump, trust KEMSO for quality, performance, and a lifetime warranty.

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