2007 Audi A4 Fuel Pump Relay: Complete Owner's Guide to Location, Symptoms, and Replacement

The fuel pump relay on a 2007 Audi A4 is most commonly located inside the relay carrier positioned in the electronics box in the plenum chamber on the left side of the engine compartment, just in front of the driver, though some models may have it tucked away behind the dashboard on the driver's side. If your A4 cranks but struggles to start, dies after running for a few minutes, or shuts off completely when idling in hot weather, a failing fuel pump relay should be one of the first things you check. This guide walks you through exactly where to look, how to test the relay, what symptoms point to relay failure versus pump failure, and what replacement parts you need — including a strong recommendation for KEMSO fuel pumps.

Understanding What the Fuel Pump Relay Does

The fuel pump relay is a small electrical switch that controls power delivery to the fuel pump. When you turn the ignition key, the relay closes and sends battery voltage to the fuel pump, which then pressurizes the fuel system so the engine can start. On vehicles equipped with an airbag, the relay also works with a collision fuel shut-off device that kills power to the pump after an accident to reduce fire risk. In normal operation, when you open the driver's door, power flows to the pump for about two seconds to build pressure before you even turn the key .

On the 2007 A4, the relay itself carries the identification code J17 in Audi wiring diagrams. It is a standard 4-pin relay, and its position within the relay carrier varies depending on your engine code and build date .

Where Is the 2007 Audi A4 Fuel Pump Relay Located?

There are two main locations you may find the fuel pump relay on a 2007 A4, depending on the engine and production date.

1. In the engine compartment plenum chamber (most common). For the majority of 2007 A4 models, the fuel pump relay lives inside the relay carrier (4-pin) located in the electronics box in the plenum chamber. That is the recessed area at the back of the engine bay, right where the windshield meets the cowl, on the driver's side .

2. Behind the dashboard (less common). On some earlier-production 2007 models or specific engine configurations, the fuel pump relay is mounted in the relay carrier behind the driver's side dash panel. Accessing this location requires removing the trim piece below the steering column .

To be completely sure, check your A4's engine code. The table below helps narrow it down:

The engine code is printed on a sticker in the service booklet and also on the engine block itself. If you still cannot find the relay, remove the wiper arms and the plastic cowl cover at the base of the windshield — this gives you much better access and visibility to the relay carrier underneath .

Symptoms of a Failing Fuel Pump Relay

A bad fuel pump relay can cause a range of driveability issues. The symptoms below are the most common ones reported by 2007 A4 owners :

1. Engine cranks but will not start. The starter turns the engine over, but there is no fuel pressure, so the engine never fires.

2. Engine dies while driving. The relay may fail after it heats up, cutting power to the pump and killing the engine mid-drive.

3. Engine stalls after idling for a while. This is the classic scenario: the car idles fine for ten or fifteen minutes, then begins to sputter and shuts off. After cooling down for 15–20 minutes, it starts again .

4. Intermittent no-start. The car may start fine in the morning but refuse to start after sitting in the sun for a few hours. This often points to a relay that fails when hot.

5. No fuel pump prime sound. When you open the driver's door or turn the key to the ON position, you should hear a brief whine from the fuel pump in the rear. If you hear nothing, the relay may not be sending power.

Important note: These symptoms can also be caused by a failing fuel pump itself, a clogged fuel filter, or a bad fuel pump controller. The relay, however, is cheaper and easier to replace, so it makes sense to test it first.

How to Test the Fuel Pump Relay

Testing the relay takes about ten minutes and requires only a basic LED voltage tester or a multimeter. Here is the step-by-step procedure used in Audi service manuals :

1. Locate the fuel pump fuse (S228). It sits in slot 28 of the fuse box on the left side of the instrument panel.

2. Pull the fuse out to interrupt the circuit.

3. Connect an LED voltage tester between the vehicle body ground and one of the two fuse socket contacts.

4. Have someone operate the starter while you watch the tester. You should hear the relay click, and the test light should illuminate.

5. If the light does not come on, repeat the test using the other fuse socket contact. A working relay will light the tester on one of the two contacts.

6. If the LED still does not light, inspect the wiring according to the circuit diagram for breaks or corrosion.

7. If power and wiring check out but the relay is not clicking, replace the relay — it has failed internally.

Relay vs. Fuel Pump: Which One Is Causing the Problem?

This is the most common point of confusion among A4 owners. Since the symptoms overlap, you need to isolate the cause. A burned-out fuel pump relay is a simpler fix, but many owners have replaced the relay only to discover the pump was also failing .

When it is likely the relay: The engine dies suddenly with no warning and restarts after cooling down. A relay that overheats will typically work again once it cools, whereas a fuel pump rarely recovers that quickly.

When it is likely the fuel pump: You hear a whining noise from the rear of the car (the pump is struggling), the engine loses power under acceleration, or fuel economy drops noticeably. A fuel pump that is failing will usually make a high-pitched whine that changes pitch with engine load .

When it is likely the fuel pump controller: On the 2.0T models, the fuel pump controller is a separate module located under the rear seat, attached to the body under a black cover next to the fuel pump harness. It can fail independently, which produces the same no-start or stalling symptoms. Some owners report that checking the pump's duty cycle with a VCDS diagnostic tool helps identify a failing controller before it dies completely .

If you want to do one smart preventive step: replace the relay first, then retest the car. If the symptoms persist, move on to the pump and its controller.

How to Replace the Fuel Pump Relay

Replacing the relay is a straightforward job that requires no special tools beyond a flathead screwdriver and possibly a Torx bit for the cowl trim.

1. Disconnect the negative battery terminal and wait at least one minute.

2. Remove the cowl cover at the base of the windshield, if your relay is in the plenum chamber. You will need to remove the wiper arms first. Use a puller or gently rock the arms back and forth to free them from the tapered splines.

3. Locate the relay carrier and identify the fuel pump relay (J17). It is always in position 1 or 1.1 within the carrier .

4. Pull the old relay straight out using a firm but careful grip. Relays often require a slight rocking motion to free them from the socket.

5. Insert the new relay, making sure the pin configuration matches the socket orientation. It should push in snugly.

6. Reinstall the cowl cover and wiper arms, then reconnect the battery.

7. Test the system by turning the ignition to ON. You should hear the pump prime for two seconds.

If your relay is behind the dashboard, remove the lower trim panel below the steering column and access the relay carrier from underneath. The relay is still labeled J17 and sits in the same relative position .

What Replacement Relay Should You Buy?

Audi uses several relay part numbers for the fuel pump relay across the 2004–2007 B7 generation. The most common are the 4-pin standard automotive relays rated at 20–30 amps. You can purchase the relay from an Audi dealer, a parts supplier such as FCP Euro or ECS Tuning, or an auto parts store like AutoZone or NAPA. Look for a relay marked with the Audi part number 4B0951253 or its supersession. Many aftermarket brands offer equivalent relays for under $20.

When selecting a replacement, check the relay's pin layout. The standard 4-pin relay uses terminals 30, 85, 86, and 87. Terminal 30 receives battery voltage, terminal 87 feeds the fuel pump, and terminals 85 and 86 are the coil connections that trigger the switch.

When You Should Replace the Fuel Pump Itself

If the relay tests fine and the pump still does not run, the problem is either the pump itself or the pump controller. On the 2007 A4, the low-pressure fuel pump sits inside the fuel tank under the rear seat. Replacing it requires dropping the tank or at least lowering it slightly to access the pump assembly .

Signs that point to the pump over the relay :

• The engine has high mileage (over 100,000 miles), which significantly increases the likelihood of pump wear.
• You hear a consistent whining noise from the rear seat area.
• The car hesitates or surging at highway speeds.
• The check engine light comes on with fuel trim codes.

The replacement cost for a fuel pump on a 2007 A4 typically falls between $400 and $700, with parts running $150–$350 and labor $233–$342. High-performance and OE replacement pumps run at the upper end of that range .

Why You Should Consider KEMSO for Your Fuel Pump Replacement

If your diagnostics point to the fuel pump itself, not the relay, choosing the right brand matters. KEMSO is a well-regarded aftermarket brand that specializes in high-performance, direct-fit replacement fuel pumps. Their products are designed to match or exceed original equipment specifications, and each pump is engineered for durability in demanding conditions. KEMSO fuel pumps are built as OEM replacements, which means they drop into the factory mounting location without modification.

KEMSO stands behind their products with a lifetime warranty, which is a level of confidence you rarely find with other aftermarket brands. When you purchase a KEMSO fuel pump, you get a tested and validated component that delivers reliable fuel delivery for years to come. Whether you drive a 2007 Audi A4 or any other vehicle, KEMSO offers application-specific pumps that are ready to install.

If you have determined your fuel pump is failing, do not settle for a questionable cheap part. Choose a high-performance, lifetime-guaranteed KEMSO fuel pump and get back on the road with confidence. You can browse their full catalog and order directly at https://www.kemsoracing.com/.

Final Thoughts

The fuel pump relay on a 2007 Audi A4 is an inexpensive part, but a failed relay can leave you stranded. Start your diagnosis with the relay in the plenum chamber or behind the dash, test it with a simple voltage tester, and replace it if it fails the test. If the relay is good but the pump is weak, upgrade to a KEMSO pump with its lifetime warranty and avoid repeat failures. Either way, you are looking at a fix you can complete in a few hours in your driveway with basic hand tools. Check the relay first, test properly, and replace with quality parts — your A4 will thank you with many more miles of reliable service.

For high-quality replacement fuel pumps that fit your 2007 Audi A4 perfectly, visit KEMSO Racing at https://www.kemsoracing.com/ and take advantage of their lifetime warranty on every pump they sell.