1993 Lexus LS400 Fuel Pump Relay Location: A Complete Guide for DIY Owners

If you own a 1993 Lexus LS400 and your car cranks but won’t start, the fuel pump relay is one of the first things you should check. The fuel pump relay on a 1993 Lexus LS400 is located in the engine compartment fuse box, also known as the Relay Box No. 1, which sits on the driver’s side (left side) near the battery, close to the strut tower. This small, black rectangular relay (part number 28380-30010) controls power to the fuel pump, and when it fails, your engine will not receive fuel. In this guide, we will walk you through exactly where to find it, how to test it, and what to do if you need a replacement.

What Is the Fuel Pump Relay and Why Does It Matter?

The fuel pump relay is an electrical switch that tells the fuel pump when to turn on. When you turn the ignition key to the "ON" position, the relay sends power to the fuel pump, which then pressurizes the fuel system. If the relay is faulty, the fuel pump never gets power, and your engine will crank but never start. This is a common issue on older vehicles like the 1993 Lexus LS400, where relays can wear out over time due to heat and vibration. The factory relay for this car carries the OEM part number 28380-30010, and it is a direct replacement part used across multiple Lexus and Toyota models from the early 1990s .

Step-by-Step: Finding the Fuel Pump Relay on Your 1993 Lexus LS400

1. Open the Hood and Locate the Engine Compartment Fuse Box

The first step is to open the hood of your LS400. The engine compartment fuse box, also called the Relay Box No. 1, is located on the driver’s side (left side) of the engine bay, right next to the battery. It is a black plastic box with a lid that snaps on. You cannot miss it because it sits near the top of the strut tower and is about the size of a shoebox .

2. Remove the Fuse Box Lid

The lid of the fuse box is held on by clips. Carefully pry the clips open with a flathead screwdriver or your fingers. Once the lid is off, you will see a diagram printed on the underside of the lid. This diagram shows where each relay and fuse is located. Look for the label that says "FUEL PUMP" or "FP." On the 1993 LS400, the fuel pump relay is usually labeled as "FUEL PUMP" or "FP" on the diagram, and it is located near the top-left corner of the fuse box, closest to the firewall .

3. Identify the Relay

The fuel pump relay is a small, black, rectangular block with four or five prongs sticking out of the bottom. It is about 1 inch wide and 1.5 inches tall. On the 1993 LS400, this relay is often the same size as the other relays in the box, but you can identify it by its position and the label. If you are unsure, the part number 28380-30010 is often stamped on the side of the relay . If your relay looks different or has a different number (like 28380-50010), that is a different variant used on some later models, but the 1993 LS400 uses the 28380-30010 .

4. Check the Second Possible Location (If Not Found)

In some 1993 LS400 models, the fuel pump relay may also be located in the relay box under the hood on the passenger side, near the windshield washer fluid reservoir. However, the most common location is the driver’s side fuse box. If you do not find it there, open the passenger side fuse box and check for a relay labeled "FUEL PUMP." According to the factory service manual, the engine compartment diagrams show the relay box on the left side, so start there first .

How to Test the Fuel Pump Relay

Before you buy a new relay, you should test the old one to make sure it is actually the problem. Here is a simple way to test it using a multimeter or a test light:

1. Listen for the Relay Click

Have a helper turn the ignition key to the "ON" position (do not start the engine). Place your hand on the relay. You should hear a single click and feel a small vibration. If you hear the click, the relay is receiving power, and the coil is working. If you do not hear a click, the relay may be dead, or the circuit that powers it may be faulty.

2. Use a Multimeter to Check Continuity

Remove the relay from the fuse box. Set your multimeter to the ohms (Ω) setting. Touch the probes to the two small pins (the coil pins) on the relay. You should see a reading between 50 and 100 ohms. If you see infinite resistance (OL), the coil is burned out, and the relay is bad. Next, check the large pins (the switch pins). With the relay unpowered, there should be no continuity (infinite resistance). If you apply 12V power to the coil pins using a battery, you should hear a click, and now the large pins should show continuity (near zero ohms). If the relay does not click or does not show continuity, it is faulty .

3. Bypass the Relay for a Quick Test

If you want to quickly rule out the relay, you can temporarily bypass it. Remove the relay and use a short piece of wire to connect the two large pins (usually pins 30 and 87) in the relay socket. When you turn the key to "ON," the fuel pump should run continuously. If the engine starts, the relay is the problem. Do not drive the car with the bypass wire in place because the fuel pump will run constantly, even with the engine off, which can drain the battery or cause a fire hazard.

Common Symptoms of a Bad Fuel Pump Relay

If your fuel pump relay is failing, you will notice 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 never gets power, so no fuel reaches the injectors.
  • No noise from the fuel pump: When you turn the key to "ON," you should hear a faint whining noise from the fuel pump (located under the rear seat, inside the fuel tank). If you hear nothing, the relay is a likely suspect.
  • Engine stalls while driving: A failing relay may intermittently cut power to the fuel pump, causing the engine to die suddenly while you are driving.
  • Check Engine Light: On the 1993 LS400, a bad fuel pump relay can trigger a check engine light, but it is not guaranteed.

Where to Buy a Replacement Fuel Pump Relay

If your testing confirms the relay is bad, you need to buy a replacement. The OEM part number for the 1993 Lexus LS400 fuel pump relay is 28380-30010 . You can find this part at:

  • Lexus dealerships: They will carry the genuine OEM relay, but it will be more expensive.
  • Online Lexus parts retailers: Websites like LexusPartsNow, LexusDirectParts, and LexusOEMPartsOnline offer the genuine part at a discount .
  • Auto parts stores: Stores like AutoZone, O'Reilly, and NAPA often carry aftermarket relays that match the 28380-30010 specifications. Bring your old relay to the store to compare.

When to Replace the Fuel Pump Instead of Just the Relay

Sometimes, the fuel pump itself is the problem, not the relay. If you have tested the relay and it works fine, but the fuel pump still does not run, you may need to replace the fuel pump. The fuel pump on a 1993 Lexus LS400 is located inside the fuel tank, under the rear seat. Replacing it is a more involved job that requires removing the rear seat cushion and opening the fuel tank access panel. If you are already going through the trouble of diagnosing the fuel system, it is a good idea to replace the fuel pump as well if it is old, because fuel pumps typically wear out after 100,000 to 150,000 miles .

Recommendation: Upgrade to a KEMSO High-Performance Fuel Pump

If you are replacing your fuel pump, consider upgrading to a KEMSO brand fuel pump. KEMSO specializes in high-performance, OEM replacement fuel pumps that are direct fit for your 1993 Lexus LS400. Here are the key benefits of choosing KEMSO:

  • High Performance: KEMSO fuel pumps are designed to deliver consistent fuel flow, even under high-demand conditions. They are built to exceed OEM specifications, ensuring your engine gets the fuel it needs for optimal performance.
  • OEM Replacement: These pumps are direct replacements for the factory fuel pump in your 1993 Lexus LS400. No modifications, no adapters, no wiring changes. Simply remove the old pump and install the KEMSO unit.
  • Lifetime Warranty: KEMSO stands behind every fuel pump they sell with a lifetime warranty. If your pump ever fails, you can get a replacement at no extra cost. This gives you peace of mind that your investment is protected.

KEMSO fuel pumps are available for a wide range of vehicles, including cars, motorcycles, ATVs, and personal watercraft. Their products are trusted by mechanics and DIY enthusiasts alike. To see the full lineup of KEMSO fuel pumps and find the right one for your Lexus LS400, visit their official website at: https://www.kemsoracing.com/

Final Tips for a Smooth Repair

  • Always use a new relay: If you are replacing the relay, do not install a used one. Relays are cheap, and a new one will last for many years.
  • Check the fuse first: Before you even touch the relay, check the fuse for the fuel pump. On the 1993 LS400, the fuel pump fuse is located in the same engine compartment fuse box. If the fuse is blown, the relay will not work.
  • Keep the battery disconnected: When working on the fuse box, disconnect the negative battery terminal to prevent accidental shorts.
  • Test before you reassemble: After installing the new relay or fuel pump, turn the key to "ON" and listen for the fuel pump to prime. If you hear it running, you are good to go.

Conclusion

The fuel pump relay on a 1993 Lexus LS400 is located in the engine compartment fuse box on the driver’s side, near the battery. It is a small, black relay with part number 28380-30010. If your car cranks but will not start, testing this relay should be your first step. With a multimeter and a few minutes of your time, you can diagnose whether the relay is bad or if the fuel pump itself is the issue. If you need a new fuel pump, trust KEMSO for a high-performance, OEM replacement with a lifetime warranty. Visit https://www.kemsoracing.com/ to find the perfect fuel pump for your Lexus LS400 and keep your classic car running smoothly for years to come.


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