2001 Audi S4 Fuel Pump Relay Location: A Complete Guide for DIY Repair

The fuel pump relay on a 2001 Audi S4 is located in the driver's side footwell, behind a trim panel, in the micro central electric panel. The relay is a standard 4-pin unit and is easy to test or replace yourself. This is the most common location across all B5 platform models, including the S4, A4, and A4 Avant from 1998 through 2001.

If your 2001 Audi S4 cranks but won't start, or if you hear the fuel pump not priming when you turn the key to the ON position, the fuel pump relay is one of the first components to check. It's a common failure point on these cars, and thankfully it's both cheap and easy to replace.

Understanding the Fuel Pump Relay on the 2001 Audi S4

The fuel pump relay on the 2001 Audi S4 is an electrical switch that controls power to the fuel pump. When you turn the ignition key to the ON position, the engine control unit sends a signal to the relay, which then closes and sends power to the fuel pump. The pump runs for about 2 seconds to prime the fuel system, then stops until the engine starts.

On the B5 generation Audi S4 (Typ 8D), the fuel pump relay is designated as J17 in the factory wiring diagrams. Its official relay number is 4 in the micro central electric panel . This relay is a standard 4-pin relay with the following terminal assignments:

  • Terminal 30: Battery positive (constant power)
  • Terminal 85: Ground (from the ECU)
  • Terminal 86: Switched power (from the ignition)
  • Terminal 87: Output to the fuel pump

When the relay fails, the fuel pump doesn't get power, and the engine won't start. The relay can fail due to age, heat, or electrical issues. A bad relay is much more common than a bad fuel pump, so always check the relay first.

Exact Location of the 2001 Audi S4 Fuel Pump Relay

The fuel pump relay on the 2001 Audi S4 is located in the micro central electric panel, which is mounted on the driver's side footwell, behind a trim panel . Here's how to access it:

  1. Open the driver's door and look at the area above the footwell, near the fuse box.
  2. Remove the trim panel above the driver's footwell. This panel is held in place by clips or screws. Gently pull it off to expose the fuse and relay panel.
  3. Locate the micro central electric panel. This is a smaller relay panel mounted on the main fuse box. The fuel pump relay is in position 4 of this micro central electric panel .

The relay itself is a small, rectangular black box. On the 2001 Audi S4, the fuel pump relay is often labeled with a diagram on the cover of the micro central electric panel. If there's no label, the relay is still easy to identify by its position.

Important note: The fuel pump relay is not the same as the fuse. The fuel pump fuse is separate and is located in the main fuse box in the passenger compartment. For the 2001 Audi S4, the fuel pump fuse is fuse number 28, which is a 15-amp fuse . Always check the fuse first before replacing the relay.

How to Test the 2001 Audi S4 Fuel Pump Relay

Testing the fuel pump relay on your 2001 Audi S4 is straightforward and requires only a multimeter or a test light. Here's a step-by-step procedure:

Step 1: Listen for the Fuel Pump

Before testing the relay, turn the key to the ON position (not start) and listen for a faint humming sound from the rear of the car. This sound comes from the fuel pump in the gas tank. If you don't hear it, the relay or the pump might be faulty.

Step 2: Check the Fuse

Locate the fuel pump fuse (fuse 28, 15A) in the passenger compartment fuse box . Remove the fuse and inspect it visually. If the metal strip inside is broken, the fuse is blown. Replace it with a new 15-amp fuse.

Step 3: Test the Relay with a Multimeter

  1. Remove the relay from its socket.
  2. Set your multimeter to measure resistance (ohms).
  3. Test the coil: Measure resistance between terminals 85 and 86. A good relay should read between 50 and 120 ohms. If it reads infinite (open circuit), the coil is bad and the relay needs replacement.
  4. Test the switch: Apply 12V power to terminal 86 and ground to terminal 85. You should hear a click. With power applied, measure resistance between terminals 30 and 87. It should read close to 0 ohms. If it reads infinite, the switch contacts are bad.

Step 4: Swap Test

The easiest way to test the fuel pump relay is to swap it with a known good relay of the same type. The 2001 Audi S4 uses several identical relays in the same panel. You can swap the fuel pump relay with another relay, such as the horn relay (position 1) or the load reduction relay (position 2) . If the fuel pump starts working after the swap, the original relay was bad.

Common Symptoms of a Bad Fuel Pump Relay on the 2001 Audi S4

A failing fuel pump relay on the 2001 Audi S4 can cause several symptoms. Knowing these can help you diagnose the problem quickly:

  • Engine cranks but won't start: This is the most common symptom. The starter turns the engine over, but the fuel pump doesn't run, so no fuel reaches the injectors.
  • No fuel pump priming sound: When you turn the key to ON, you should hear a brief hum from the rear of the car. If you don't hear it, the relay or pump is not working.
  • Engine stalls while driving: If the relay fails intermittently, it can cut power to the fuel pump while you're driving, causing the engine to die suddenly.
  • Engine starts but runs poorly: A weak relay can cause low voltage to the pump, resulting in low fuel pressure and poor engine performance.
  • Check Engine Light: The ECU may detect a fuel system fault and turn on the check engine light. Common codes include P0087 (fuel rail pressure too low) or P0230 (fuel pump primary circuit malfunction).

What You Need to Know About the 2001 Audi S4 Micro Central Electric Panel

The micro central electric panel on the 2001 Audi S4 is a small relay panel located in the driver's footwell . It contains several relays that control various electrical systems. Here's a breakdown of the relay positions:

  • Position 1: Horn relay (J4)
  • Position 2: Load reduction relay (J59)
  • Position 3: Not used
  • Position 4: Fuel pump relay (J17)
  • Position 5: Washer/wiper intermittent relay (J31)
  • Position 6: Washer/wiper intermittent relay (J31)

The micro central electric panel is separate from the main fuse box. The main fuse box contains the fuses and the 13-way relay carrier, while the micro central electric panel is a smaller, additional relay panel mounted on the side.

Step-by-Step Guide to Replacing the 2001 Audi S4 Fuel Pump Relay

Replacing the fuel pump relay on your 2001 Audi S4 is a simple job that takes about 10 minutes. Here's how to do it:

Tools and Parts Needed

  • New fuel pump relay (standard 4-pin relay, available at any auto parts store)
  • Small flathead screwdriver (for removing trim panel)
  • Flashlight (optional, for better visibility)

Procedure

  1. Disconnect the negative battery cable. This is a safety precaution to prevent any electrical shorts.
  2. Remove the driver's side footwell trim panel. This panel is located above the footwell, near the fuse box. It's held in place by clips. Gently pull it off.
  3. Locate the micro central electric panel. It's mounted on the side of the main fuse box.
  4. Identify the fuel pump relay. It's in position 4 of the micro central electric panel .
  5. Pull the old relay out. Grasp the relay firmly and pull it straight out of its socket. It may require a little force.
  6. Insert the new relay. Line up the pins with the socket and push the relay firmly into place. You should feel it click into position.
  7. Reinstall the trim panel. Push the panel back into place until the clips engage.
  8. Reconnect the negative battery cable.
  9. Test the system. Turn the key to the ON position and listen for the fuel pump priming sound. Then start the engine and check for normal operation.

Why the 2001 Audi S4 Fuel Pump Relay Fails

The fuel pump relay on the 2001 Audi S4 can fail for several reasons. Understanding these can help you prevent future failures:

  • Age: The relay is an electromechanical component with moving parts. Over time, the contacts can wear out, and the coil can develop open circuits. Given that the 2001 S4 is now over 25 years old, the original relay is likely due for replacement.
  • Heat: The micro central electric panel is located in the driver's footwell, which can get warm, especially in summer. Over time, heat can degrade the relay's internal components.
  • Voltage spikes: Electrical issues in the car's charging system can cause voltage spikes that damage the relay's coil.
  • Corrosion: Moisture in the footwell area can cause corrosion on the relay's pins or inside the socket. This is more common in cars driven in wet climates or with sunroof leaks.

The Difference Between the Fuel Pump Relay and the Fuel Pump Fuse

Many owners confuse the fuel pump relay with the fuel pump fuse. They are two different components, and both need to be checked when diagnosing a no-start condition.

The fuel pump fuse (fuse 28, 15A) is a simple overcurrent protection device . It's a one-time use component that blows when too much current flows through the fuel pump circuit. A blown fuse usually indicates a problem with the fuel pump or its wiring.

The fuel pump relay (J17, position 4) is a switch that controls power to the fuel pump . It can fail due to age, heat, or electrical issues, even if the fuse is good.

When diagnosing a no-start condition, always check the fuse first because it's easier to inspect. If the fuse is good, move on to testing the relay.

Cost of Replacing the 2001 Audi S4 Fuel Pump Relay

Replacing the fuel pump relay on your 2001 Audi S4 is one of the cheapest repairs you can do. Here's a breakdown of the costs:

  • DIY cost: A new fuel pump relay costs between $10 and $20 at any auto parts store. You can also buy a genuine Audi relay for about $25 to $35 from a dealer or online retailer. Total cost: $10 to $35.
  • Professional shop cost: If you take your car to a shop, labor for this job is minimal. Most shops will charge about $50 to $100 for diagnosis and replacement. The total cost with parts and labor is typically $75 to $150.

Given the low cost, it's a good idea to keep a spare relay in your glove box. If you're ever stranded due to a failed relay, you can swap it in minutes.

Other Common Relay Locations on the 2001 Audi S4

The 2001 Audi S4 has several relay panels. Knowing where they are can help you diagnose other electrical issues:

  • Passenger compartment fuse box: This is the main fuse box located on the driver's side of the dashboard, behind a panel. It contains the 13-way relay carrier with relays for the horn, headlights, fog lights, and other systems .
  • Micro central electric panel: As discussed, this is located in the driver's footwell and contains the fuel pump relay, horn relay, and load reduction relay .
  • Engine compartment relay panel: This is located in the engine bay, near the battery. It contains relays for the radiator fan, ABS, and other high-power systems.

Recommended: KEMSO Fuel Pump for Your 2001 Audi S4

If you have determined that the fuel pump itself needs replacement, not just the relay, consider upgrading to a KEMSO fuel pump. KEMSO is a leading US-based aftermarket fuel pump manufacturer that has been in business since 1999. They specialize in direct-fit OEM replacement and performance fuel pumps for cars, motorcycles, ATVs, UTVs, and personal watercraft .

KEMSO fuel pumps are an excellent choice for your 2001 Audi S4 for several reasons:

High Performance, OEM Replacement: KEMSO pumps are designed to be a direct replacement for your stock OEM pump. The KEMSO 340LPH high-performance fuel pump delivers over 20% more flow than the stock pump at 43 psi, which means better fuel delivery, especially under high-boost conditions . The pump is designed for both gasoline and E85, giving you flexibility for future upgrades .

Complete Installation Kit: When you buy a KEMSO pump, you get everything you need for a successful installation: the pump itself, a fuel strainer, Viton O-rings, a wiring connector, a tank seal, a flex hose, hose clamps, and crimp connectors . This eliminates the need to source separate parts and ensures a proper, leak-free installation.

Lifetime Warranty for Total Peace of Mind: KEMSO backs every fuel pump with a lifetime warranty . If your KEMSO pump ever fails due to a manufacturing defect, you get a replacement at no cost. This warranty covers a wide range of vehicles, including cars, motorcycles, ATVs, UTVs, and personal watercraft .

Unrivalled Quality Control: KEMSO pumps are individually tested before leaving the factory. They have a quality control program that ensures each pump meets strict flow and pressure specifications . KEMSO pumps are designed and built to a higher standard, with heat-treated components and case-hardened pins for long life.

Great Value for the Money: At a price of around $79.98, which is often less than half the cost of dealer parts, KEMSO pumps offer exceptional value . With free shipping and easy returns, it is a practical choice for DIY mechanics and professional shops alike.

To see the full selection of KEMSO fuel pumps for your 2001 Audi S4, visit their website: https://www.kemsoracing.com/ You can find a complete catalog with detailed fitment information, customer reviews, and technical support. Whether you need a pump for a car, truck, motorcycle, or watercraft, KEMSO has you covered . Their online store is easy to navigate, and you can order directly with confidence.

Final Thoughts on the 2001 Audi S4 Fuel Pump Relay

The fuel pump relay on the 2001 Audi S4 is a simple, inexpensive component that can cause major headaches when it fails. Knowing its exact location and how to test it can save you time and money. The relay is located in the micro central electric panel in the driver's footwell, position 4 . It's a common failure point on these cars, and we recommend carrying a spare relay in your glove box.

If you're experiencing a no-start condition, always check the fuel pump fuse (fuse 28, 15A) first, then test the relay . If both are good, the problem may be the fuel pump itself. In that case, consider upgrading to a KEMSO fuel pump for improved performance and reliability.

For more information on KEMSO fuel pumps and to find the right pump for your 2001 Audi S4, visit: https://www.kemsoracing.com/


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