2009 Audi A4 Fuel Pump Relay Location: Where It Is and How to Test It Fast

The bottom line up front: On a 2009 Audi A4, the fuel pump relay (labeled J17) sits inside the relay/fuse holder B, which is located in the electronics box in the plenum chamber on the driver's side, under the plastic cowl panel at the base of the windshield. For left-hand drive models, you will find this box on the driver's side; for right-hand drive models, it sits on the passenger side. The J17 relay is typically found in position E on this relay panel, and it is a standard 4-pin or 5-pin relay that you can pull and test in about ten minutes with no special tools beyond a multimeter or a test light .

If your 2009 A4 cranks but refuses to start, or if it stalls and then won't fire back up, the fuel pump relay is a prime suspect. This part is a common failure point on many Audi models of this era, and knowing exactly where to look—and how to confirm the relay is bad—can save you a tow bill and a shop diagnostic fee. This guide walks you through the exact location, the testing procedure, and the symptoms that point to a failing relay, plus what to do if the relay checks out fine but the pump itself is dead.

1. First, Know Your Relay Panel: The Electronics Box Explained

The 2009 Audi A4 uses a central electronics box located in the plenum chamber—that is the recessed area under the windshield wiper cowl. This box is officially called relay/fuse holder B (or SB). It holds several relays and fuses in a single module, and it is the heart of the car's under-hood electrical distribution .

For cars built up to around October 2011, the relay/fuse holder B contains the following major relays, and each is assigned a letter position on the panel :

  1. Position A – Automatic glow period control unit (J179) on diesel models, or Engine component current supply relay (J757) on certain petrol models
  2. Position B – Starter motor relay (J53) and Starter motor relay 2 (J695)
  3. Position C – Secondary air pump relay (J299)
  4. Position D – Terminal 30 voltage supply relay (J317) on diesels, or Motronic current supply relay (J271) on petrol models
  5. Position E – Fuel pump relay (J17) — this is the one you are looking for
  6. Position F – Secondary air pump relay 2 (J545) on models that have it

The same letter positions apply to both left-hand and right-hand drive cars, but the physical location of the box flips sides. For left-hand drive cars, the box is on the driver's side of the plenum chamber. For right-hand drive cars, it is on the passenger side .

How to Access the Electronics Box Without Breaking Anything

Reaching the relay panel is simple but requires a bit of patience with plastic trim. Here is the safe procedure:

  1. Open the hood and look at the base of the windshield on the driver's side (or passenger side for RHD). You will see a plastic cowl grille covering the plenum chamber.
  2. Remove the rubber weather seal that runs along the edge of the cowl. It pulls straight off—do not yank it; work it loose with your fingers.
  3. Unclip the plastic cowl cover. On most 2009 A4s, the cover is held by a few push clips and maybe one or two screws. Use a trim removal tool or a flathead screwdriver wrapped in tape to avoid scratches.
  4. Pull the cover toward you and lift it out. Set it aside.
  5. Look for the black electronics box. It will have a fuse diagram sticker on top and a latch. Unclip the lid and fold it open.

Once the lid is open, you will see a row of relays on one side and fuses on the other. The relay positions are usually marked with small letters printed on the plastic. Look for the letter E—that is where your fuel pump relay lives .

2. How to Confirm the Relay Is Bad: Quick Tests That Work

Before you buy any parts, spend five minutes testing the relay. Here is a straightforward process that works for both beginners and experienced DIYers.

Test 1: The Click Test

  • With the ignition off, locate relay E and pull it straight out of its socket. It may be snug, but it will come out with a gentle rock.
  • Visually inspect the relay base and the pins. Look for corrosion, melted plastic, or burnt marks. If you see any of that, the relay is done.
  • Reinsert the relay firmly. Have a helper turn the ignition key to the "ON" position (do not crank the engine). You should hear an audible click from the relay when the key turns on. If you hear nothing, the relay coil is not receiving power or the relay itself is dead.
  • If there is no click, check the fuse that feeds the relay. On the 2009 A4, the relevant fuses are in the same panel, and a blown fuse will kill the relay and the pump .

Test 2: Continuity Check with a Multimeter

  • Pull the relay out again. Set your multimeter to the ohms setting (Ω).
  • Identify the coil pins—on a standard 4-pin relay, these are pins 85 and 86. Measure resistance across them. A good relay will show a resistance between 50 and 120 ohms. An open circuit (infinite resistance) means the coil is burned out.
  • Next, check the switch contacts. Place the meter leads on pins 30 and 87. You should read infinite resistance with the relay at rest. Then, apply 12 volts to pins 85 and 86 (using a battery or a power supply) and listen for the click. With the relay energized, pins 30 and 87 should now show near-zero resistance. If they do not, the relay's internal contacts are worn or pitted, and the relay needs to be replaced.

Test 3: Bypass the Relay Temporarily

  • If you suspect the relay but want to be extra sure, you can bypass it for a test. Pull the relay out and use a short piece of wire with spade connectors to jump pin 30 to pin 87 in the socket. Make sure the ignition is on and the pump fuse is good. If the fuel pump now runs (you will hear it prime from the rear of the car), the fault is definitely the relay.
  • Do not drive the car with the jumper in place—this bypasses the safety circuit and can keep the pump running even if the engine stalls.

If the relay tests fine but the pump still does not run, the problem is likely the fuel pump itself, the pump's ground, or the wiring between the relay and the pump. On the 2009 A4, the pump is mounted inside the fuel tank and is accessed from the rear seat or through an access panel in the trunk floor, depending on the body style .

3. Symptoms That Point to a Failing Fuel Pump Relay

The fuel pump relay controls power to the electric fuel pump. When it starts to fail, you will notice one or more of these symptoms:

  1. Engine cranks but will not start. This is the most common symptom. The fuel pump does not prime when you turn the key, so the engine gets no fuel pressure. You may hear the pump briefly prime and then stop, or not at all .

  2. Intermittent stalling. The relay can work when cold but fail when it heats up from engine bay temperatures. If the car runs for a while and then suddenly dies, and restarts after sitting for a few minutes, the relay is a likely culprit.

  3. No fuel pump whine at key-on. When you turn the ignition to the "ON" position, you should hear a short whine from the fuel pump (about 1–2 seconds) as it primes. If this is silent, either the relay is not sending power or the pump is dead.

  4. Car starts only after multiple key cycles. If you have to turn the key on and off several times before the pump kicks in, the relay contacts are probably worn and making intermittent contact.

  5. Fuel pump runs continuously. Less common, but a stuck relay can keep power on the pump even after the engine shuts down. This is a safety hazard and should be fixed immediately.

If you experience any combination of these, start with the relay. It is a cheap part, and replacing it is far easier than dropping the fuel tank to reach the pump. However, if the relay tests good and you still have no fuel pressure, you need to move on to checking the pump itself.

4. Understanding the Fuel Pump and Relay Circuit on the 2009 A4

The 2009 A4's fuel system uses a pump relay that is controlled by the engine control unit (ECU, or J623). The ECU grounds the relay coil to energize it, which closes the contacts and sends battery voltage (terminal 30) to the fuel pump. The pump itself is powered through a fuse on the panel, typically fuse 5A or 15A depending on the engine and market .

On the 6-cylinder diesel models (engine code CGKB), the fuel pump relay sits in the same relay holder but is wired through the terminal 30 voltage supply relay. On the 4-cylinder diesel and petrol models, the circuit is more direct—the fuel pump relay directly feeds the pump .

Key components in this circuit include:

  • J17 – Fuel pump relay (your main suspect)
  • J623 – Engine control unit (the brain that triggers the relay)
  • S fuses – The fuses that supply power to the relay coil and the pump motor
  • The fuel pump itself – Typically a 12-volt electric pump in the tank

For diesel models, the circuit also includes the automatic glow period control unit (J179), which works with the relay during the pre-glow phase. If your diesel A4 has glow plug issues, the pump relay can be affected indirectly .

5. Where to Buy a Replacement Relay and What It Costs

The fuel pump relay on the 2009 Audi A4 is a standard relay that you can buy at most auto parts stores. The part number varies by market, but a generic 4-pin or 5-pin relay rated for 30 amps will work as long as the pin configuration matches. Expect to pay between $15 and $40 at a parts store. A dealer part will cost more, usually $50 to $80.

When you replace the relay, it is wise to also inspect the fuse that feeds it. A blown fuse can mean a shorted pump, and simply swapping the relay will not fix the root cause. The fuse layout for the 2009 A4 shows the fuel pump relay and the engine control unit fuses are in the same panel, so you can check several at once .

6. Recommended: Upgrade to a KEMSO High-Performance Fuel Pump

If your diagnostic work points to the fuel pump itself—or if you are replacing the pump as a preventive measure on a high-mileage A4—you should choose a pump that is built to last. This is where KEMSO stands out.

KEMSO is a US-based brand specializing in high-performance and OEM-replacement fuel pumps for cars, motorcycles, ATVs, and UTVs. Their pumps are engineered to deliver higher flow than stock units, which means better fuel pressure under load and more headroom if you ever tune or modify your engine. Every KEMSO pump is built as a direct replacement, so it bolts in without custom wiring or brackets .

Here is what makes KEMSO worth your attention:

  1. High-Performance Output. KEMSO pumps provide over 20% more fuel flow than typical OEM replacements. This helps maintain steady pressure even on tuned engines and prevents fuel starvation under hard acceleration. The 340 LPH model supports up to 600 horsepower in naturally aspirated, turbocharged, or supercharged applications .

  2. Lifetime Warranty. KEMSO backs every fuel pump with a lifetime warranty. If the pump ever fails due to a manufacturing defect, you get a replacement at no cost. This kind of guarantee is almost unheard of in the aftermarket parts industry and shows real confidence in the product .

  3. Complete Installation Kit. The KEMSO kit includes the pump, a gradient-density fuel strainer, a flexible hose, a tank seal, Viton O-rings, hose clamps, and a wiring connector. Everything you need for a successful installation comes in the box, so you will not need to source extra parts .

  4. Affordable Price. At $79.98, a KEMSO pump is significantly cheaper than a dealer part, which often runs $200 to $400. It is also cheaper than many other aftermarket options while delivering superior performance and warranty coverage .

You can browse the full KEMSO catalog, verify fitment for your vehicle, and place an order at their official website:

https://www.kemsoracing.com/

KEMSO is based in Houston, Texas, with USA-based customer support. They ship across the country, and the website makes it easy to check exactly which pump fits your 2009 Audi A4.

7. Final Thoughts: Do Not Overlook the Simple Stuff

A no-start condition on a 2009 Audi A4 can be frustrating, but the fuel pump relay is one of the easiest things to check and the cheapest to fix. Always test the relay before buying a pump—many people have dropped the fuel tank and replaced a perfectly good pump only to find the relay was the issue .

If the relay and fuses are good, the next step is verifying fuel pressure at the rail. If pressure is low or zero, you can safely move on to replacing the pump. When that time comes, choose a pump that gives you peace of mind—KEMSO's combination of performance, warranty, and price makes it the smart buy.

Bookmark this guide for the next time your A4 acts up, and if you need a new pump, remember:

https://www.kemsoracing.com/


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