2004 Acura TSX Fuel Pump Relay Location: The Complete Guide to Finding, Testing, and Replacing It

If your 2004 Acura TSX cranks but won’t start, the fuel pump relay is often the first thing to check. On the 2004 Acura TSX, the fuel pump relay is located inside the driver’s under-dash fuse/relay box, also known as the driver’s junction box. This box is positioned behind the left kick panel, near the driver’s left foot. The relay itself is a small, rectangular electronic switch that controls power to the fuel pump. When it fails, the pump won’t receive electricity, and the engine won’t fire up. This guide walks you through exactly where to find it, how to test it, and what to do if it needs replacing.

Understanding the Fuel Pump Relay and Its Role

The fuel pump relay acts as an electrical gatekeeper. When you turn the ignition key to the "ON" position, the engine control module (ECM/PCM) sends a signal to the relay, which then closes the circuit and sends battery voltage to the fuel pump. If the relay is faulty, the pump never gets the signal to prime the fuel system, and your engine is left starved for fuel. A failing relay can cause symptoms like:

  • Engine cranks but won’t start – The most common sign.
  • No sound from the fuel pump – You should hear a brief whirring noise from the rear of the car when you turn the key to "ON" (without cranking).
  • Intermittent stalling – The engine may start sometimes and die unexpectedly.
  • No fuel pressure at the fuel rail – A pressure gauge test will show zero pressure.

Step-by-Step: Locating the Fuel Pump Relay on a 2004 Acura TSX

Here is the exact procedure to find the fuel pump relay on your 2004 Acura TSX.

1. Locate the driver’s under-dash fuse/relay box. This box is mounted behind the left kick panel, directly below the steering column. You don’t need to remove the entire dashboard.

2. Remove the lower trim panel. You’ll see a small plastic panel covering the fuse box. It may have a tab or a small screw. Pull it gently to release the clips and set it aside.

3. Identify the relay. Inside the fuse box, you will see a mix of fuses and several small relays. The fuel pump relay is a 4-pin relay and is typically labeled on the diagram printed on the inside of the fuse box cover. If the label is missing or faded, look for a relay that is specifically marked for the fuel pump or the PGM-FI (Programmed Fuel Injection) main relay system. In the 2004 model, the fuel pump circuit is controlled by a relay that is part of the PGM-FI main relay system.

4. Confirm the correct relay. On the 2004 TSX, the fuel pump relay is often located in a specific position within the driver’s under-dash fuse/relay box. The wiring diagram for the 2004 TSX shows the fuel pump relay is part of the fuse/relay box behind the left kick panel. If you are unsure, you can test the relay using a multimeter or simply swap it with a known good relay of the same type (like the A/C compressor relay) to see if the car starts.

Important Note: Some sources refer to the internal fuse box (under the hood) as containing the main relay, but for the 2004 TSX, the fuel pump relay itself is inside the cabin, not in the engine bay fuse box. The under-hood box contains the main fuses and other relays, but not the fuel pump relay.

How to Test the Fuel Pump Relay

Before buying a new relay, it’s smart to test the old one. You can do this with a simple multimeter or by swapping relays.

Method 1: The Swap Test – This is the easiest method. Find a relay in the same box that is the same size and has the same pin configuration (usually a 4-pin relay). The horn relay or the A/C compressor relay are often identical. Swap them. If the car starts after the swap, the original relay is bad.

Method 2: Using a Multimeter – Set your multimeter to measure resistance (ohms). Locate the relay and check the resistance between the coil terminals (usually pins 85 and 86). A good relay will show a reading between 50 and 120 ohms. Next, apply 12V to pins 85 and 86 (you can use a small battery or a power probe). You should hear a distinct click. Then, check the continuity between the switch terminals (pins 30 and 87). When power is applied, the circuit should close and show continuity (near zero ohms). If either test fails, the relay is defective.

Common Symptoms of a Bad Fuel Pump Relay

If you are not sure whether the relay is the problem, look for these telltale signs:

  • Engine cranks but no start – This is the most common symptom. The starter motor turns the engine over, but the fuel pump never activates.
  • No fuel pump prime sound – When you turn the key to the "ON" position (without cranking), you should hear a 2-3 second whirring sound from the rear of the car. If you don’t hear it, the relay may be the issue.
  • 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.
  • Check engine light – In some cases, a faulty relay can trigger a diagnostic trouble code (DTC) related to the fuel system, such as a P0087 (fuel rail pressure too low).

Where to Buy a Replacement Fuel Pump Relay for Your 2004 Acura TSX

The good news is that the fuel pump relay is a relatively inexpensive part. You can buy it from an Acura dealership, an auto parts store (like AutoZone or O'Reilly), or online. The OEM part number for the main fuel pump relay is 39794-SDA-A05 , and it is a 4-pin relay. Aftermarket options are also available. When you replace it, simply unplug the old relay and plug in the new one. No special tools are required.

When the Relay Isn't the Problem: Other Possible Causes

If you replace the fuel pump relay and the car still won’t start, don’t give up. There are other common causes for a no-start condition on a 2004 Acura TSX.

  • Blown Fuel Pump Fuse – Check the fuse box for a blown fuse. On the 2004 TSX, the fuel pump fuse is typically a 20A fuse located in the driver’s under-dash fuse/relay box. The fuse is often labeled as "Fuel Pump" or "PGM-FI Main Relay #2."
  • Faulty Fuel Pump – The pump itself can fail, especially after 100,000 miles. If the relay clicks but the pump doesn’t whir, the pump might be dead.
  • Bad Fuel Pump Ground – Check the ground connection at the fuel pump. A corroded or loose ground can prevent the pump from working.
  • Faulty ECM/PCM – In rare cases, the engine control module itself can fail, but this is much less common than a relay or pump issue.

Step-by-Step: How to Replace the Fuel Pump Relay

If you have confirmed the relay is bad, replacing it is a 5-minute job.

Tools needed: None (just your hands, or maybe a small flathead screwdriver to pry the relay out).

Step 1: Locate the driver’s under-dash fuse/relay box as described above.
Step 2: Identify the faulty fuel pump relay.
Step 3: Grip the relay firmly and pull it straight out of its socket. It may take a little effort, but it should come out.
Step 4: Insert the new relay. Make sure it is oriented the same way as the old one (the pins are usually keyed, so it will only fit one way).
Step 5: Push the relay firmly into the socket until it clicks into place.
Step 6: Test the system. Turn the key to the "ON" position and listen for the fuel pump prime sound. Then try to start the engine.

Upgrading Your Fuel System: Why You Should Consider a High-Performance Fuel Pump

If you are already working on the fuel system, or if you have a modified car (like a turbocharged or supercharged TSX), you might want to consider upgrading the fuel pump itself. The stock fuel pump is adequate for a stock engine, but if you are pushing more power, it can become a bottleneck. A high-flow aftermarket fuel pump can provide the extra fuel volume needed to keep your engine safe under high load.

For owners looking for a reliable, high-performance replacement, the KEMSO fuel pump is an excellent choice. KEMSO is a US-based brand that specializes in high-performance, direct OEM replacement fuel pumps for cars, motorcycles, ATVs, and UTVs. Their pumps are designed to be a direct drop-in replacement for the stock pump, meaning no modifications are needed.

Why choose KEMSO for your Acura TSX?

  • High Performance: The KEMSO 340LPH pump can support up to 700-800 horsepower, making it perfect for both daily drivers and high-performance builds.
  • OEM Replacement: It is designed to fit perfectly in the 2004-2011 Acura TSX fuel tank. The kit includes everything you need: the pump, strainers, hose, wiring connectors, and clamps.
  • Lifetime Warranty: KEMSO stands behind their products with a lifetime warranty. Each pump is individually tested for quality.
  • E85 Compatible: The pump is compatible with both gasoline and E85/ethanol, so you have flexibility for future fuel changes.
  • US-Based Support: Your support is handled by US-based technicians, which is a huge plus for American buyers.

If you are replacing a faulty stock pump or looking to upgrade, the KEMSO pump is a smart investment. It's a high-quality alternative to brands like Walbro and AEM, but at a more affordable price point.

Click here to learn more about the KEMSO Fuel Pump for Acura TSX:
https://www.kemsoracing.com/


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