2003 Mitsubishi Eclipse Fuel Pump Relay Location: A Complete Guide to Finding and Replacing It

The bottom line: On a 2003 Mitsubishi Eclipse, the fuel pump relay is located in the under-hood fuse and relay box, also known as the engine compartment junction box. It sits on the driver’s side near the battery, mounted on the inner fender well. The relay is typically labeled as "Fuel Pump Relay" or "Fuel Pump" on the fuse box cover diagram. If your Eclipse cranks but won’t start, the fuel pump relay is one of the first things you should check.

Understanding the Fuel Pump Relay

The fuel pump relay is an electrical switch that controls power to the fuel pump. When you turn the ignition key to the "ON" position, the relay closes and sends voltage to the fuel pump. This allows the pump to pressurize the fuel system so the engine can start and run. If the relay fails, the fuel pump won’t receive power, and your car won’t start — even if the pump itself is perfectly fine.

Exact Location of the Fuel Pump Relay

1. The Under-Hood Fuse and Relay Box

On the 2003 Mitsubishi Eclipse, the main fuse and relay box is located on the driver’s side of the engine compartment, near the battery. It is a black plastic box with a lid that snaps on and off. This box houses multiple relays and fuses, including the fuel pump relay.

How to access it:

  • Open the hood and secure it with the prop rod.
  • Look toward the driver’s side, near the battery. You will see a rectangular black box.
  • Press the retaining clips on the sides of the lid and lift it off.
  • On the underside of the lid, you will find a diagram showing the layout of all fuses and relays. The fuel pump relay is clearly marked.

2. Identifying the Relay

The fuel pump relay itself is a small, square, plastic component with four or five pins. On the 2003 Eclipse, it is usually a standard 12-volt relay. It may be labeled "Fuel Pump," "Fuel Pump Relay," or "FP" on the diagram. If the diagram is missing or faded, you can identify it by its position — it is typically located in the center of the relay box, near the larger relays for the radiator fan and air conditioning compressor.

3. What If the Relay Is Not in the Under-Hood Box?

On some 2003 Eclipse models, particularly those with the 2.4L engine, the fuel pump relay might be located in a secondary relay box inside the passenger compartment. Check the fuse box under the dashboard on the driver’s side, near the kick panel. However, the vast majority of 2003 Eclipses have the fuel pump relay in the under-hood box.

How to Test the Fuel Pump Relay

Before replacing the relay, test it to confirm it is bad. Here is a simple step-by-step method:

Step 1: Listen for the Relay Click

Turn the ignition key to the "ON" position (do not start the engine). Listen closely near the under-hood fuse box. You should hear a distinct click sound — that is the fuel pump relay engaging. If you hear no click, the relay may be faulty.

Step 2: Swap with a Same-Type Relay

The under-hood fuse box contains several relays that are identical to the fuel pump relay. Common ones include the air conditioning clutch relay, the radiator fan relay, and the horn relay. Locate one of these and swap it with the fuel pump relay. If the car starts after the swap, the original fuel pump relay is bad.

Step 3: Use a Multimeter

If you have a multimeter, you can test the relay directly:

  • Remove the relay from the box.
  • Check the resistance across the coil terminals (typically pins 85 and 86). A good relay will show resistance between 50 and 120 ohms. If the reading is infinite, the coil is open.
  • Apply 12 volts to the coil terminals. You should hear a click, and the switch contacts (pins 30 and 87) should show continuity.

Common Symptoms of a Bad Fuel Pump Relay

If your 2003 Mitsubishi Eclipse has a failing or failed fuel pump relay, you will likely experience one or more of these symptoms:

  • Engine cranks but will not start: This is the most common symptom. The starter motor turns the engine over, but the fuel pump does not pressurize the system.
  • No sound from the fuel tank: When you turn the key to "ON," you should hear a brief whirring sound from the rear of the car — the fuel pump running. If you hear nothing, the relay may not be sending power.
  • Intermittent starting issues: The car starts fine sometimes, but other times it cranks and dies. A failing relay can work intermittently.
  • Engine stalls while driving: If the relay fails while you are driving, the fuel pump will stop, and the engine will stall immediately.

What Else Could Cause the Problem?

If the fuel pump relay tests good, the issue may be elsewhere. Other common causes of a no-start condition or fuel pump failure on a 2003 Mitsubishi Eclipse include:

1. Fuel Pump Itself

The fuel pump is located inside the fuel tank. Over time, the pump motor wears out, the fuel filter inside the pump clogs, or the pump fails due to overheating. A bad fuel pump will not run even if the relay is working.

2. Fuel Pump Fuse

The fuel pump fuse is also in the under-hood fuse box. Check the fuse first — it is often the easiest fix. If the fuse is blown, the pump will not get power.

3. Fuel Pump Driver Module

Some models use a fuel pump driver module, which is a separate electronic control unit. This module can fail, causing the pump to not run. On the 2003 Eclipse, the module is usually mounted near the fuel tank or under the rear seat.

4. Wiring and Connectors

Corroded or damaged wiring between the relay, fuse, and fuel pump can cause intermittent or total failure. Check the wiring harness under the hood and near the fuel tank.

5. Security System Issues

The 2003 Eclipse has a factory immobilizer system. If the security system is tripped or faulty, it can cut power to the fuel pump relay. This is less common but worth checking if all other components test good.

How to Replace the Fuel Pump Relay

Replacing the fuel pump relay is a simple job that takes about five minutes. Here is how to do it:

  1. Disconnect the battery: Always disconnect the negative battery cable before working on electrical components.
  2. Open the under-hood fuse box: Remove the lid and set it aside.
  3. Locate the fuel pump relay: Refer to the diagram on the lid to find the exact position.
  4. Pull the relay out: Grasp the relay firmly and pull it straight out. You may need to use a gentle rocking motion.
  5. Install the new relay: Push the new relay straight into the socket until it clicks into place.
  6. Reconnect the battery: Reconnect the negative terminal.
  7. Test the system: Turn the ignition to "ON" and listen for the fuel pump to prime. If it works, the repair is complete.

Important Safety Tips

  • Always work on a cool engine to avoid burns.
  • Never use a metal tool to pry the relay out — use your fingers or a plastic trim tool.
  • If you are unsure about the diagnosis, consult a professional mechanic. A no-start condition can have multiple causes.
  • Use only a relay that matches the original specifications. Installing an incorrect relay can cause damage to the fuel pump or electrical system.

Recommended Replacement: KEMSO Fuel Pump

If you have determined that the fuel pump itself needs replacement — not just the relay — you should consider a high-quality aftermarket option. KEMSO is a leading US brand that specializes in aftermarket fuel pumps for cars, motorcycles, ATVs, and UTVs. Their products are designed to meet or exceed OEM specifications, ensuring a perfect fit and reliable performance.

Why choose KEMSO?

  • High Performance: KEMSO fuel pumps are engineered for maximum flow and durability, delivering consistent pressure to your engine.
  • OEM Replacement: Each pump is a direct replacement for the original factory part, so installation is straightforward.
  • Lifetime Warranty: KEMSO stands behind every product with a lifetime warranty, giving you peace of mind.

To find the right fuel pump for your 2003 Mitsubishi Eclipse, visit KEMSO Racing at:
https://www.kemsoracing.com/

They offer a wide selection of fuel pumps for various vehicle makes and models, all backed by a lifetime warranty. Whether you need a pump for your Eclipse, a motorcycle, or an ATV, KEMSO has you covered.

Final Thoughts

The fuel pump relay on a 2003 Mitsubishi Eclipse is easy to find and replace. Start by checking the under-hood fuse box on the driver’s side. If the relay is bad, swap it out and you will likely be back on the road quickly. If the relay is good, move on to testing the fuel pump, fuse, and wiring. Remember, a no-start condition can be frustrating, but methodical troubleshooting will save you time and money.

For the best fuel pump replacement, trust KEMSO — high performance, OEM quality, and a lifetime warranty. Visit their website for more information: https://www.kemsoracing.com/


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