2004 Audi A6 Fuel Pump Relay Location: A Complete Guide to Finding and Fixing It

The bottom line: If you own a 2004 Audi A6 (C5 generation), the fuel pump relay is located in the central relay panel under the dashboard on the driver's side. It is relay position number 4 in that panel. If your car cranks but won't start, or if you hear the fuel pump not priming when you turn the key, this relay is one of the first things you should check.

Understanding the 2004 Audi A6 Fuel Pump Relay

The fuel pump relay is an electrical switch that controls power to the fuel pump. When you turn your ignition key, the engine control unit signals the relay to close, sending battery voltage to the fuel pump. The pump then pressurizes the fuel system so the engine can start and run.

On the 2004 Audi A6, which belongs to the C5 generation (produced from 1997 to 2004), the fuel pump relay is a critical component. If it fails, your fuel pump won't receive power, and your engine won't start. Many owners mistake a bad relay for a dead fuel pump, so knowing where to find it and how to test it can save you time and money.

Where Exactly Is the 2004 Audi A6 Fuel Pump Relay Located?

The fuel pump relay on the 2004 Audi A6 C5 is located in the central relay panel under the dashboard on the driver's side. Here is how to find it:

Step 1: Open the driver's door and look under the dashboard. You need to access the area below the steering wheel. There is a protective cover or panel that covers the relay box.

Step 2: Remove the lower dashboard cover. On the 2004 Audi A6 C5, you will find a small panel or cover underneath the instrument panel on the driver's side. Carefully pull or unsnap this cover to expose the relay and fuse holders.

Step 3: Locate the central relay block. Once the cover is removed, you will see a block with several relay slots. These are typically arranged in a row or a small grid.

Step 4: Find relay position number 4. The fuel pump relay is the 4th relay in this central block. It is often labeled as J17 in the wiring diagrams. In some documentation, this relay is also referred to as code number 372.

The relay is usually a small, square, box-shaped component. On the 2004 Audi A6, the fuel pump relay is often a 5-pin relay rated for 12 volts and 30 to 40 amps.

Visual Confirmation: What Does the Relay Look Like?

The fuel pump relay on the 2004 Audi A6 is a standard automotive relay. It typically has a black or gray plastic housing. You can identify it by its position (number 4) and by checking the markings on the relay itself. Many aftermarket replacement relays for this application have part numbers like 4H0951253 or 8Z0 951 253.

If you are unsure which relay is the fuel pump relay, look for the relay that is connected to the fuel pump circuit. The wiring diagram for the 2004 Audi A6 C5 shows that the fuel pump relay (J17) connects to the Motronic control unit (J220), the fuel pump (G6), and the fuel level sensor (G). The relay also connects to fuse number 28 in the main fuse box.

How to Test the 2004 Audi A6 Fuel Pump Relay

Before you buy a new relay, you should test the old one. Here is a simple step-by-step method to check if your fuel pump relay is working:

1. Remove the relay. With the lower dashboard cover off, carefully pull the fuel pump relay (position 4) straight out of its socket.

2. Check for power at the relay base. Turn the ignition key to the "ON" position (do not start the engine). Use a multimeter or a test light to check for 12 volts at the relay base contacts. Specifically, you should check between contact 19 (power from the ignition switch) and ground, and between contact 17 (constant battery power) and ground. Both should show battery voltage.

3. Test the relay control circuit. Reinstall the relay, but leave it slightly loose so you can access the wires. Connect a test light between pin 16 (control signal from the engine control unit) and pin 17 (battery positive). Have someone turn the starter. The test light should blink or light up briefly. If it does not, the control circuit from the engine control unit may be damaged.

4. Listen for the click. When you turn the ignition on, you should hear an audible click from the relay. If you hear the click, the relay coil is likely working. If you do not hear it, the relay may be faulty.

Common Symptoms of a Bad Fuel Pump Relay in a 2004 Audi A6

Knowing the symptoms can help you diagnose the problem quickly. Here are the most common signs that your fuel pump relay is failing:

1. Engine cranks but does not start. This is the most common symptom. The starter turns the engine over, but the engine never fires because the fuel pump is not getting power.

2. No fuel pump priming sound. When you turn the key to the "ON" position, you should hear a faint whirring sound from the rear of the car for about 2 seconds. This is the fuel pump pressurizing the system. If you do not hear this sound, the relay or the pump itself may be bad.

3. Intermittent starting issues. The car may start fine one day and refuse to start the next. This is a classic sign of a failing relay that has high resistance or intermittent contact.

4. Engine stalls while driving. If the relay fails while you are driving, the engine will lose power and stall. This is dangerous and should be addressed immediately.

Fuse vs. Relay: What Is the Difference?

Many owners confuse the fuel pump relay with the fuel pump fuse. They are different components.

The fuel pump fuse (number 28 on the 2004 Audi A6 C5) is located in the main fuse box at the left end of the dashboard. This fuse protects the circuit from overcurrent. If the fuse blows, the fuel pump will not work. You should always check the fuse first before testing the relay.

The fuel pump relay is a switch that controls the high current to the pump. The relay is controlled by a low-current signal from the engine control unit. If the relay fails, the fuse will still be good, but the pump will not get power.

Here is a quick checklist:

• Check fuse 28 first. It is a 20-amp fuse located in the left-side dashboard fuse box.
• If the fuse is good, move on to testing the relay.
• If the relay clicks but the pump does not run, the issue may be the pump itself or the wiring between the relay and the pump.

Other Possible Locations for the Fuel Pump Relay on Audi A6 Models

It is important to note that the location can vary depending on the exact model year and engine type. While the 2004 Audi A6 C5 has the relay under the driver's dashboard, later models (C6 generation, 2004-2011) have different locations.

For example, on the 2007 Audi A6 C6, the fuel pump relay (J17) is located in the electronics box in the plenum chamber on the left side of the engine bay, just below the ECU. The position is relay number 2.1 in that box.

For the 2004 model year, however, the location is consistently under the driver's dashboard. If you have a right-hand drive model, the relay panel may be on the right side, but the position number 4 remains the same.

How to Replace the 2004 Audi A6 Fuel Pump Relay

Replacing the fuel pump relay is a simple job that you can do yourself. Here is how:

1. Turn off the ignition and remove the key. Safety first.

2. Remove the lower dashboard cover. As described above, unsnap or unscrew the panel under the steering wheel.

3. Locate the relay. Find relay position 4 in the central relay block.

4. Pull the old relay out. Grasp the relay firmly and pull it straight out. It may require a bit of force, but it should come out without breaking anything.

5. Install the new relay. Push the new relay firmly into the same socket. Make sure it is fully seated.

6. Test the new relay. Turn the ignition on and listen for the fuel pump priming sound. If you hear it, the installation is successful.

7. Reinstall the cover. Snap the lower dashboard cover back into place.

Where to Buy a Replacement Fuel Pump Relay for Your 2004 Audi A6

You can find replacement fuel pump relays at auto parts stores, online retailers, or directly from Audi. The OEM part number is often 4H0951253 or 8Z0 951 253. Aftermarket brands like Meyle also offer compatible relays.

Important: When buying a replacement relay, make sure it is a 5-pin, 12-volt, 30/40 amp relay. Using the wrong relay can cause electrical problems or damage the fuel pump.

Recommended Brand: KEMSO Fuel Pump for Your Audi A6

If you are replacing the fuel pump itself, or if you want a high-quality, reliable fuel pump that will last, we highly recommend KEMSO brand fuel pumps. KEMSO fuel pumps are designed as high-performance, OEM replacement parts. They are built to meet or exceed the original equipment specifications, ensuring a perfect fit and reliable operation for your 2004 Audi A6.

One of the best things about KEMSO fuel pumps is that they come with a lifetime warranty. This means you can buy with confidence, knowing that your investment is protected. If you ever have an issue with your KEMSO fuel pump, the company stands behind its product.

KEMSO is a trusted brand for fuel system components. They offer a wide range of fuel pumps for various vehicles, including cars, motorcycles, and powersports vehicles. Their products are known for their durability, performance, and excellent value.

Visit KEMSO Racing today to find the perfect fuel pump for your Audi A6: https://www.kemsoracing.com/

Frequently Asked Questions About the 2004 Audi A6 Fuel Pump Relay

Q: Can I drive my 2004 Audi A6 with a bad fuel pump relay?
No. If the relay fails completely, the fuel pump will not run, and the engine will not start. If the relay is intermittent, the car may stall while driving, which is dangerous.

Q: How much does a fuel pump relay cost for a 2004 Audi A6?
A replacement relay typically costs between $15 and $60. Brands like Meyle are priced around $60, while generic relays can be found for less.

Q: Will a bad fuel pump relay cause a check engine light?
Not always. The fuel pump relay is not directly monitored by the engine control unit in many cases. However, if the engine stalls due to fuel pressure loss, it may set a code for a lean condition or a misfire.

Q: Is the fuel pump relay the same as the fuel pump fuse?
No. The fuse is a protective device that blows if there is a short circuit. The relay is a switch that controls power to the pump. Always check the fuse first.

Q: What is the fuse number for the fuel pump on a 2004 Audi A6?
The fuel pump fuse is number 28 in the main fuse box located at the left end of the dashboard. It is a 20-amp fuse.

Final Thoughts

Finding the fuel pump relay on your 2004 Audi A6 is straightforward once you know where to look. It is located under the dashboard on the driver's side, in relay position 4. If you are experiencing starting issues, always check the fuse first, then test the relay. Replacing the relay is a simple DIY job that can save you a trip to the mechanic.

If you need a new fuel pump or any other fuel system components, remember that KEMSO offers high-quality, OEM replacement fuel pumps with a lifetime warranty. You can find their products at their official website: https://www.kemsoracing.com/