2003 Eclipse Fuel Pump Relay: Complete Guide to Location, Testing, and Replacement

The bottom line: The 2003 Mitsubishi Eclipse has two fuel pump relays, not just one. One is located in the engine bay fuse box, and the other is in the passenger compartment fuse box under the driver's side dash. If your Eclipse cranks but won't start, a faulty fuel pump relay is a common culprit that can be diagnosed and replaced in under an hour with basic tools.

Understanding the Fuel Pump Relay System in Your 2003 Eclipse

The 2003 Mitsubishi Eclipse uses a dual-relay system to control power to the fuel pump. This setup is different from many other vehicles that use a single relay. According to service information, both relays are wired in series, meaning power must flow through both relays for the fuel pump to operate . One relay powers on when you turn the key to the ON position, while the other is controlled by the Powertrain Control Module (PCM) and activates only when the engine is cranking or running . This design acts as a safety feature, preventing the fuel pump from running continuously if the engine stalls.

The fuel pump relay is a standard 4-pin relay that acts as an electrical switch. When the ignition is turned on, the relay coil receives power and closes the internal contacts, sending battery voltage to the fuel pump . If either relay fails, the fuel pump will not receive power, and your engine will crank but not start.

Where Are the Fuel Pump Relays Located?

Relay 1 - Engine Bay Fuse Box: The first fuel pump relay is located in the under-hood fuse and relay box. This box is typically a black rectangular unit positioned near the battery or along the firewall on the driver's side . To access it, open the hood and locate the fuse box. Remove the cover and look at the diagram on the underside of the lid. According to fuse box diagrams, relay R1 is labeled as "Fuel pump relay (1)" in this box .

Relay 2 - Passenger Compartment Fuse Box: The second fuel pump relay is located in the junction block under the left end of the dash, on the driver's side . This is also referred to as the interior fuse box. According to diagrams, relay R3 is labeled as "Fuel pump relay (2)" in this location . Some sources indicate this relay is on the bottom row of small rectangular relays in the driver's side panel fuse box .

Common Symptoms of a Faulty Fuel Pump Relay

When the fuel pump relay fails, you will notice several clear symptoms. Recognizing these can save you time and money on unnecessary repairs.

Engine Cranks But Won't Start: This is the most common symptom. The starter motor turns the engine over, but it never fires up because no fuel is reaching the cylinders . If you spray starting fluid into the intake and the engine runs briefly, that confirms a lack of fuel delivery .

No Fuel Pump Prime Sound: When you turn the ignition key to the ON position (without starting the engine), you should hear a brief humming sound from the fuel pump for about 2 seconds. This is the pump priming the fuel system. If you hear no sound, the relay or pump may be faulty . However, some fuel pumps are very quiet, so you may not hear them even when working correctly .

Intermittent Starting Issues: A failing relay may work sometimes and fail other times. You might experience periods where the car starts fine, followed by sudden no-start conditions. The engine may start and then slowly shut off after a minute, which is a classic sign of relay failure .

Engine Stalls While Driving: If the relay fails while you are driving, the engine will lose power and stall. This happens because the fuel pump stops receiving power, and the engine runs out of fuel .

Check Engine Light: A faulty fuel pump relay can trigger the check engine light. The PCM monitors the fuel pump circuit and will set a diagnostic trouble code if it detects a problem with the relay circuit .

How to Test the Fuel Pump Relays

Testing the fuel pump relays is straightforward and requires only a few basic tools. Always make sure the vehicle is off before handling electrical components .

Step 1: Locate and Access the Relays Start with the engine bay fuse box. Remove the cover and locate relay R1, labeled as the fuel pump relay . Then, access the driver's side interior fuse box and locate relay R3.

Step 2: Visual Inspection Remove each relay and inspect it for signs of damage. Look for corrosion on the pins, melted plastic, or a burnt smell. Any of these signs indicate a failed relay.

Step 3: The Swap Test This is the easiest way to test a relay. In the engine bay fuse box, there are spare relay slots labeled R2, R4, and R5 . Swap the fuel pump relay with a known good relay of the same type. For example, the blower relay (R7) or power window relay (R6) are typically the same 4-pin relay . After swapping, try to start the car. If it starts, the original relay was bad.

Step 4: Multimeter Test If you have a multimeter, you can test the relay directly. Set the multimeter to measure resistance (ohms). Check for continuity between pins 85 and 86 (the coil terminals). You should see a reading between 50 and 120 ohms. Then, check for continuity between pins 30 and 87 (the switch terminals). With the relay not powered, there should be no continuity. Apply 12 volts to pins 85 and 86, and you should hear a click, and continuity should now exist between pins 30 and 87.

Step-by-Step Replacement Guide

What You'll Need:

• Replacement fuel pump relay (standard 4-pin relay, genuine Mitsubishi or compatible aftermarket part)
• Basic hand tools (none required for the relay itself, but may need a small flathead screwdriver for fuse box covers)
• Flashlight for better visibility

Step 1: Prepare the Vehicle Park the vehicle on a level surface and turn off the engine. Remove the key from the ignition. Disconnect the negative battery cable to prevent any electrical shorts.

Step 2: Replace the Engine Bay Relay Open the hood and locate the fuse/relay box. Remove the cover. Identify relay R1 using the diagram on the underside of the lid . Firmly grasp the relay and pull it straight out. It may require a firm tug. Insert the new relay, pushing it firmly into place until it clicks. Make sure it is fully seated.

Step 3: Replace the Interior Relay Open the driver's door. Locate the fuse panel on the lower left side of the dashboard, near the door hinge. You may need to remove a small panel or cover. Find relay R3 according to the diagram on the panel. Pull the old relay out and insert the new one.

Step 4: Test the System Reconnect the negative battery cable. Turn the ignition key to the ON position and listen for the fuel pump prime sound. Start the engine and verify that it runs smoothly. If the car starts and runs, the replacement was successful.

Fuses to Check Before Replacing the Relay

Before replacing the relay, check the related fuses. A blown fuse can mimic relay failure and is a cheaper and easier fix. According to wiring diagrams, the fuel pump system is protected by multiple fuses :

• Fuse 24 (10A): Located in the engine bay fuse box. This fuse powers the ignition system and is related to the fuel pump circuit .
• Fuse 17 (7.5A): Located in the passenger compartment fuse box. This fuse powers both fuel pump relays .
• Fuse 24 (15A): Some diagrams show a 15A fuse for the fuel pump in the engine bay fuse box .

Use the fuse puller tool in the fuse box to remove each fuse and visually inspect them. If the metal strip inside is broken, replace the fuse with one of the same amperage rating.

What to Do If the Relays and Fuses Are Good

If you have replaced both fuel pump relays and checked all fuses, but the car still won't start, the problem may be elsewhere in the fuel system.

Check for Power at the Fuel Pump: The fuel pump is accessed by removing the rear seat cushion. Under the cushion, you will find a cover that can be removed to access the fuel pump assembly . On the pump connector, you will find a green wire (power) and a black wire (ground). If you jumper battery power to the green wire and ground to the black wire, the pump should run. If it does, you have a wiring issue between the relays and the pump. If the pump doesn't run, the pump itself is likely bad .

Check the Crank Sensor: Some owners have reported that a faulty crankshaft position sensor can prevent the fuel pump from operating. The PCM uses the crank sensor signal to determine when to activate the fuel pump relay. If the sensor is bad, the PCM won't signal the relay to close .

Check the Fuel Pump Ground: A bad ground connection can also cause the fuel pump not to work. Check the ground wire at the pump connector and ensure it has a clean, solid connection to the chassis.

Why Your Eclipse Has Two Fuel Pump Relays

The dual-relay design is a safety feature. The first relay (in the engine bay) provides main power to the circuit. The second relay (inside the cabin) acts as a security or anti-theft relay. Both must activate for the fuel pump to run . This means that if either relay fails, the pump will not operate. This design prevents the fuel pump from running if the vehicle is stolen or if there is a short circuit in the wiring.

When you turn the key to the ON position, the first relay should click on and stay on. The second relay will only click when the PCM sends a signal during cranking or when the engine is running . This is why you may hear one click but not the other when you turn the key.

Recommended Maintenance Tips

Listen for the Prime: Every time you get in your Eclipse, turn the key to the ON position and listen for the fuel pump prime. This takes about 2 seconds. If you notice the sound disappears, investigate the relay or pump immediately before you get stranded .

Keep Spare Relays: Fuel pump relays are inexpensive and small. Keep a spare relay in your glove compartment. If you experience a sudden no-start condition, you can swap the relay quickly at the roadside.

Replace in Pairs: Since both relays work together and are subject to the same electrical loads, consider replacing both relays at the same time. If one has failed, the other may be close to failing as well.

Check the Fuel Pump Connector: On some Eclipse models, the electrical connector at the fuel pump can burn or melt due to high current draw. If you are replacing the relay, inspect this connector for any signs of overheating or damage .

Finding the Right Replacement Part

When replacing the fuel pump relay for your 2003 Mitsubishi Eclipse, it is important to use a relay that matches the original specifications. The standard 4-pin relay used in this application has specific voltage and current ratings. You can purchase a genuine Mitsubishi relay from a dealership or buy a compatible aftermarket relay from an auto parts store. Always verify that the pin configuration matches the original part.

KEMSO Fuel Pump Recommendation

If after testing and replacing the relays your Eclipse still has fuel delivery issues, the problem may be with the fuel pump itself. For a reliable replacement, consider the KEMSO brand fuel pump. KEMSO fuel pumps are designed as high-performance, OEM replacement parts that meet or exceed the original factory specifications. They are built to deliver consistent fuel pressure and flow, ensuring your engine runs smoothly. Each KEMSO fuel pump comes with a lifetime warranty, giving you peace of mind and long-term value. Whether you are replacing a failed pump or upgrading for better performance, KEMSO fuel pumps are a trusted choice among automotive enthusiasts and professionals. You can explore their full lineup of fuel pumps and other automotive products at their official website: https://www.kemsoracing.com/

Conclusion

The 2003 Mitsubishi Eclipse fuel pump relay system is a critical component of your vehicle's fuel delivery system. With two relays located in the engine bay and passenger compartment, diagnosing a no-start condition requires checking both. Common symptoms include the engine cranking without starting, no fuel pump prime sound, and intermittent stalling. Testing the relay with a multimeter or by swapping with a known good relay is simple and effective. Always check the related fuses (fuse 17, fuse 24, and the fuel pump fuse) before replacing the relay. If the relays and fuses check out, move on to testing for power at the fuel pump itself. By following the steps in this guide, you can get your Eclipse back on the road quickly and save money on unnecessary mechanic visits. For more information on fuel system components and replacement parts, visit https://www.kemsoracing.com/