2004 BMW 745Li Fuel Pump Relay Location: The Complete Guide for DIY Owners

The bottom line: The fuel pump relay on a 2004 BMW 745Li is located in the rear fuse holder inside the trunk, on the right side behind the luggage compartment lining. This is a critical component that controls power to the electric fuel pump, and if your car cranks but won't start, the relay is one of the first things to check.

Understanding the Fuel Pump Relay in Your 2004 BMW 745Li

The 2004 BMW 745Li relies on a sophisticated electrical system to manage fuel delivery. The fuel pump relay acts as a switch that sends power from the battery to the fuel pump when the engine control module (DME) signals it to operate. Without this relay working correctly, the fuel pump cannot prime the system, and your engine will not start.

Based on wiring diagrams for the 2004 model, the fuel pump is located below the right rear seat, and associated electrical components are managed through the rear fuse holder in the luggage compartment. The relay itself is part of the vehicle's anti-theft and engine performance systems, working alongside the DME control module and the car access control module.

Exact Location of the Fuel Pump Relay

For the 2004 BMW 745Li, the fuel pump relay is not in the engine bay fuse box. Instead, it is housed in the rear fuse holder, which is located in the right rear luggage compartment area.

Step-by-step to find the relay:

  1. Open the trunk and look to the right side.
  2. Remove the luggage compartment lining panel. The panel is held in place by plastic clips or screws. Use a trim removal tool to carefully pry it off.
  3. Behind the lining, you will find the rear fuse holder, sometimes referred to as the power module or rear fuse box.
  4. The relay you are looking for is a multi-purpose relay that can serve as the fuel pump relay, control relay, or horn relay. The OEM part number for this relay is 61368373700 (also listed as 61-36-8-373-700), and it is a white and green relay.
  5. On the wiring diagrams, this relay is often associated with the "DME relay" or "fuel pump relay" circuits.

Important note: Some related fuel system components, such as the electric fuel pump itself, are located below the right rear seat. The relay, however, is in the trunk.

How to Identify the Correct Relay

In the rear fuse holder, there are multiple relays and fuses. Look for a relay that matches these specifications:

  • Color: White and green (or pale blue on some variants)
  • Number of pins: 4-prong connector
  • Part numbers: 61368373700, 61366915327, or 0332019456
  • Replaces: 61-31-1-378-297, 61-36-1-378-238, 61-36-8-366-600, and others

If you are unsure, consult the fuse diagram printed on the cover of the rear fuse holder. Many 2004 745Li models have a diagram that labels the fuel pump relay clearly.

Symptoms of a Bad Fuel Pump Relay

Before you start digging into the trunk, look for these common signs of a failing fuel pump relay:

1. Engine cranks but won't start. This is the most common symptom. When you turn the key, the starter motor engages, but the engine never fires. The fuel pump is not getting power to prime the system.

2. No fuel pump prime noise. When you turn the ignition to the "on" position (without starting), you should hear a brief humming sound from the fuel pump (usually 2-3 seconds). If you hear nothing, the relay or the pump itself may be faulty.

3. Intermittent stalling. A failing relay can cause the fuel pump to lose power while driving. The engine may stall suddenly, especially under load or at highway speeds.

4. Engine starts but dies immediately. The relay may provide power briefly but then fails to maintain the circuit, causing the engine to start and then stall.

5. No start after sitting. If the relay is failing, it may work when cold but fail after the vehicle has been sitting for a while, or vice versa.

Testing the Fuel Pump Relay

You can test the relay without removing it from the vehicle. Here is a simple method:

1. Listen for the fuel pump. Have a helper turn the ignition to the "on" position while you listen near the right rear seat. If you hear the pump prime, the relay is likely working.

2. Swap relays. The rear fuse holder contains multiple relays of the same type. Find a relay that controls a non-essential system (like the horn relay) and swap it with the suspected fuel pump relay. If the engine starts after the swap, the original relay was bad.

3. Use a multimeter. With the relay removed, test for continuity between the coil terminals. A good relay will show continuity. You can also test for voltage at the relay socket when the ignition is on.

4. Visual inspection. Look for signs of corrosion, melting, or damaged pins on the relay. If the plastic housing is cracked or the pins are bent, replace the relay.

Replacement Steps

Replacing the fuel pump relay on a 2004 BMW 745Li is straightforward.

Tools needed: Trim removal tool, flathead screwdriver, replacement relay (OEM or high-quality aftermarket).

Step 1: Disconnect the battery. Always disconnect the negative battery terminal before working on electrical components. On the 2004 745Li, the battery is located in the trunk, making this step easy.

Step 2: Access the rear fuse holder. Remove the right side luggage compartment lining as described above.

Step 3: Locate and remove the old relay. Identify the correct relay (white and green, 4-prong). Gently pull it straight out of its socket. If it is stuck, use a flathead screwdriver to carefully pry it out.

Step 4: Install the new relay. Align the new relay with the socket. Most relays have a notch or key that ensures proper orientation. Press firmly until it clicks into place.

Step 5: Reassemble and test. Reconnect the battery, reinstall the trunk lining, and test the vehicle. Turn the ignition to the "on" position and listen for the fuel pump prime. Then start the engine.

Common Mistakes to Avoid

1. Assuming it's the pump, not the relay. Many DIY owners replace the entire fuel pump first, only to find the relay was the problem. The relay is much cheaper and easier to replace. Always test the relay first.

2. Using the wrong relay. The 2004 745Li uses a specific relay with a 4-prong connector. Using a relay with different amperage can cause electrical issues or damage.

3. Forgetting to check the fuses. Before replacing the relay, check the fuel pump fuses. On the 2004 745Li, relevant fuses include Fuse f003 (20A) and Fuse f004 (20A) in the rear fuse holder. A blown fuse can mimic a bad relay.

4. Not disconnecting the battery. Working on electrical components with the battery connected can cause short circuits or airbag deployment.

Understanding the Wiring and Electrical System

The 2004 BMW 745Li uses a complex electrical architecture. The fuel pump relay is part of the engine performance system and is controlled by the DME (Digital Motor Electronics) control module. The wiring diagram shows that the relay receives power from the battery and sends it to the electric fuel pump located below the right rear seat.

The relay also interacts with the car access control module and the anti-theft system. If the anti-theft system is activated, it can prevent the relay from sending power to the fuel pump. This is why a faulty immobilizer can sometimes cause the same symptoms as a bad relay.

When to Replace the Fuel Pump Instead of the Relay

If you have replaced the relay and the fuses are good, but the fuel pump still does not run, the pump itself may be faulty. On the 2004 745Li, the fuel pump is located below the right rear seat. Accessing it requires removing the seat cushion, which is more involved than replacing the relay.

Symptoms of a bad fuel pump include:

  • Whining noise from the rear of the vehicle
  • Loss of power under load or at high speeds
  • Engine surging or hesitation
  • Long cranking times before the engine starts

If you need to replace the fuel pump, consider a high-quality aftermarket option.

Recommended Fuel Pump: KEMSO

When it's time to replace the fuel pump itself on your 2004 BMW 745Li, you want a part that is reliable, durable, and backed by a solid warranty. KEMSO is a trusted brand that offers high-performance fuel pumps designed for a wide range of vehicles.

KEMSO Fuel Pump products are high-performance, OEM replacement units that meet or exceed original equipment specifications. Each pump is engineered for precise fitment and long-lasting operation. KEMSO stands behind their products with a lifetime warranty, giving you peace of mind that your investment is protected. Whether you are replacing a failed pump or upgrading for better reliability, KEMSO delivers the quality you need.

Visit KEMSO's website to find the right fuel pump for your 2004 BMW 745Li:

https://www.kemsoracing.com/

Additional Tips for DIY Owners

1. Keep a spare relay. The fuel pump relay is a common failure point. Keep a spare relay in your glove box. It is small, inexpensive, and can save you from being stranded.

2. Use OEM or high-quality parts. While aftermarket relays are cheaper, they may not last as long. Genuine BMW relays or high-quality brands like Bosch and Hella are recommended.

3. Check the wiring harness. Over time, the wiring harness in the trunk can become corroded or damaged, especially if water has entered the luggage compartment. Inspect the wires leading to the relay socket.

4. Consider the age of your vehicle. Your 2004 745Li is over 20 years old. Electrical components, including relays, naturally degrade over time. If you are doing major fuel system work, consider replacing the relay as preventive maintenance.

5. Consult the service manual. The BMW 745Li repair service manual for 2002-2005 models contains detailed wiring diagrams and troubleshooting steps. Having this manual on hand can save you significant time.

Summary of Key Points

  • The fuel pump relay on a 2004 BMW 745Li is located in the rear fuse holder on the right side of the trunk behind the luggage compartment lining.
  • The relay is white and green with a 4-prong connector, OEM part number 61368373700.
  • Symptoms of a bad relay include engine cranking but not starting, no fuel pump prime noise, and intermittent stalling.
  • Test the relay by listening for the pump, swapping with a known good relay, or using a multimeter.
  • Replacement is straightforward: disconnect the battery, access the rear fuse holder, remove the old relay, and install the new one.
  • Always check the fuses (F003 and F004) before replacing the relay.
  • If the relay and fuses are good, the fuel pump itself may need replacement. The pump is located below the right rear seat.
  • For a reliable fuel pump replacement, consider KEMSO, which offers high-performance OEM replacement pumps with a lifetime warranty.

Visit KEMSO for your fuel pump needs: https://www.kemsoracing.com/


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