1999 Lexus GS300 Fuel Pump Relay Location (Exactly Where to Find It & What to Do)

The fuel pump relay in your 1999 Lexus GS300 is located inside the passenger side footwell fuse/relay box. You must remove the lower dash panel (kick panel) to access it.

That is the straightforward answer you need if you're diagnosing a fuel pump issue or a non-starting engine. Knowing where the relay is is just the first step. Understanding how to access it, identify it, test it, and replace it is crucial for solving fuel delivery problems on your GS300. Let's break down everything you need to know.

Finding the Relay: Step-by-Step Access

  1. Prepare the Vehicle: Park the GS300 on a level surface. Engage the parking brake firmly. Turn the ignition OFF and remove the key.
  2. Disconnect the Battery (Strongly Recommended): Locate the negative (-) terminal on the battery in the engine bay. Using a 10mm wrench or socket, loosen the clamp nut and carefully lift the negative cable off the terminal. Secure it away from the terminal to prevent accidental contact. This prevents electrical shorts and potential sparks while working near fuses and relays.
  3. Locate the Passenger Side Lower Dash Panel (Kick Panel): Move to the front passenger seat area. Look down and towards the front of the footwell. You'll see a large, roughly rectangular plastic panel running vertically along the side of the footwell, covering the area under the glove compartment and extending down to the floor. This panel is held in place by clips and usually one or two screws at the bottom (near the floor mat/carpet).
  4. Remove the Panel:
    • If screws are present near the bottom edge, remove them using a Phillips screwdriver or appropriate socket/bit.
    • Carefully pry the panel away from the dash structure starting at the bottom or sides. Use your fingers or a wide, flat trim tool to avoid damaging the clips or the panel itself. Work around the edges, releasing each clip.
    • Once all clips are free, angle the panel out and set it aside.
  5. Identify the Fuse/Relay Box: With the kick panel removed, you will see a black or gray plastic box mounted to the side of the dashboard structure – this is the passenger footwell junction block.
  6. Remove the Cover: The box will have a removable cover. Look for a latch, tab, or retaining screw. Release the latch/pull the tab/remove the screw and lift the cover straight off. Set it aside safely.
  7. Locate the Fuel Pump Relay: Inside the box, you'll see an array of fuses (mostly smaller, colored plastics) and several larger cube-shaped components – these are the relays. The relays are typically black cubes, 1 to 1.5 inches square. You need to identify the correct one:
    • Diagram is Key: Look for the fuse/relay layout diagram. This is often printed on the inside surface of the cover you just removed or sometimes on a sticker adhered to the fuse box itself near the lid opening.
    • Standard Labeling: On a 1999 Lexus GS300, the fuel pump relay is commonly labeled as "FUEL PUMP" or "FUEL PMP" or sometimes just "EFI" (Electronic Fuel Injection – which powers the ECU and fuel pump relay circuit). Be precise – don't confuse it with other similar relays like "C/OPN" (Circuit Open) which is for door locks/windows, or the main "ECU" relay.
    • Position Confirmation: Diagrams for this model year typically place the fuel pump relay in the top row or upper section of the relay block within this passenger footwell box. Find the relay that matches the diagram label for "FUEL PUMP".
    • Visual Check: The relay itself is a standard ISO micro relay common in many cars of the era. It will have four or five blade terminals protruding from the bottom, visible when you look at the relay socket.

Identifying the Relay Visually (Once Found)

While the diagram is essential for initial location, confirming by label and type is important:

  • ISO Micro Relay: The fuel pump relay in the 1999 GS300 is a standard black plastic ISO 280 Micro Relay. Key features:
    • Roughly 1 inch (25mm) cube shape.
    • Four or five blade terminals on the bottom.
    • Usually has markings like "DENSO" (OEM manufacturer) and a part number (e.g., 056700-, 28300-**). Common replacement numbers include TYCO V23134-B2-X044 or equivalents like Bosch 0 332 332 450. The diagram label "FUEL PUMP" is the primary identifier in the box.

Why Finding the Fuel Pump Relay Matters

The fuel pump relay is an electro-mechanical switch controlled by the Engine Control Unit (ECU). Its job is vital:

  1. Receives Signal: When you turn the ignition key to "ON" or "START," the ECU sends a signal to the relay coil.
  2. Completes High-Current Circuit: This signal energizes the coil, pulling internal switch contacts closed. This closes the high-current (amperage) circuit between the main power source (battery) and the fuel pump.
  3. Powers the Fuel Pump: High-current flows through the closed relay contacts, down the power wire to the fuel pump located in the fuel tank. The pump pressurizes the fuel rail.
  4. Sustains Operation: After the initial prime, the ECU keeps the relay energized as long as the engine is running or cranking (assuming proper signals from engine sensors like the crankshaft position sensor). If you turn the ignition off or crash, the ECU cuts power via the relay.
  5. Protection: The relay protects the ECU from handling the high current required by the fuel pump directly. It acts as a buffer.

Symptoms Pointing to a Bad Fuel Pump Relay (or Related Issues)

A failing relay is a common culprit for fuel pump problems:

  • Engine Cranks But Won't Start: The most frequent symptom. The starter turns the engine over, but the engine never fires because no fuel is being delivered.
  • Engine Stalls Suddenly While Driving: A relay that fails intermittently or overheats can cut power to the fuel pump instantly.
  • Engine Stalls and Won't Restart Immediately: May restart after cooling off if the relay failure is heat-related.
  • No Fuel Pump Priming Sound: When you turn the ignition key to "ON" (before cranking), you should hear a distinct whirring or buzzing sound for a few seconds from the rear (fuel tank area). No sound strongly suggests a relay, fuse, wiring, or pump issue.
  • Clicking Sound from Relay Area: A faint, rapid clicking from the passenger footwell fuse box when cranking or with ignition ON can sometimes indicate a weak/failing relay coil, but it could also be other relays operating normally. Don't rely solely on this sound.

Testing the Fuel Pump Relay (Critical Step)

Never just replace the relay because you found it! Proper testing confirms if it's the problem or if you have a deeper issue (like wiring, fuse, pump, or ECU problem). You need basic tools: test light or digital multimeter (DMM).

Method 1: The Swap Test (Simplest for DIY)

  1. Find Identical Relay: Locate another relay in the same passenger footwell fuse box that looks identical to the fuel pump relay (same size/shape/terminal count). Common candidates are the C/Open (Circuit Open Relay) or sometimes the Horn relay. Consult your fuse box diagram to find a non-critical one. Do not swap with the main ECU relay.
  2. Swap Relays: Carefully pull the suspected fuel pump relay and the known good identical relay straight out. Swap their positions in the fuse box sockets.
  3. Check Operation: Turn the ignition to "ON." Listen carefully at the rear wheel/fuel tank area for the pump priming sound. If it now primes, the original fuel pump relay is likely faulty. Try starting the car. If it starts, the relay was the problem.
  4. Interpretation: If the problem (no prime/no start) persists and you are confident the relay you swapped in is functional (e.g., the horn works if you swapped the horn relay, power locks work if you swapped C/Open relay), then the problem lies elsewhere (fuse, wiring, fuel pump, pump ground, ECU signal, etc.). Note: This test confirms the relay was bad if swapping fixes the problem but does not definitively prove a swapped-in relay is good if the problem remains – it's primarily a test for the original relay.

Method 2: Testing with a Test Light/DMM

This tests if power is reaching the relay and leaving it correctly. You need access to the relay pins with it plugged in.

  1. Locate the Relay Socket: The relay plugs into a socket with exposed metal terminals surrounding the blades. The diagram often identifies the function of each terminal in the socket (e.g., "85", "86", "87", "30").
  2. Identify Terminal Functions (Use Diagram!): Most ISO relays follow a standard:
    • Terminals 85 & 86: Coil control circuit (Low current). One should get power with ignition ON, the other is usually ground.
    • Terminal 30: High-current feed from the battery (via a fuse - the EFI fuse under the hood!).
    • Terminal 87: High-current output to the fuel pump.
    • (Less common - Terminal 87a: Not used in standard fuel pump applications).
  3. Test Power Feed to Terminal 30:
    • Set DMM to DC Volts 20V scale or use test light.
    • Ignition OFF. Clip the negative probe of DMM (or test light clip) to a solid unpainted metal point (ground).
    • Touch the positive probe (or test light point) to terminal 30 socket contact. Should read battery voltage (approx 12.6V OFF, 13.5-14.8V with engine running) constantly, regardless of ignition position. If NO voltage here: Check the EFI fuse in the engine bay main fuse box.
  4. Test Ignition Signal & Ground at Coil (Terminals 85/86):
    • Ignition OFF. Test terminal 85: Connect one DMM probe to terminal 85 socket contact. Connect other probe to battery ground. Set DMM to Ohms or Continuity. Should be open (infinite resistance/no beep). If it reads continuity directly to ground before applying power, the coil ground might be shorted (less common, but possible).
    • Ignition ON. Retest terminal 85: Should now show continuity to ground (0 ohms or continuity beep). This confirms the ECU is providing the ground path for the coil when commanded.
    • Test terminal 86: With ignition ON, test voltage between terminal 86 socket contact and ground. Should read battery voltage (approx 12V). This is the switched ignition power feeding the other side of the coil.
    • Conclusion: If terminals 85 and 86 have the correct readings (ground path closed by ECU and +12V power) with ignition ON, the control side is working. If either fails, the problem is upstream (wiring, ECU, ignition switch).
  5. Test Relay Output (Terminal 87):
    • If Control Side Tests Good (Step 4): With ignition ON or during cranking, test voltage between terminal 87 socket contact and ground.
    • Expectation: Should read battery voltage during the fuel pump prime cycle (few seconds at ignition ON) and continuously while cranking. If you get voltage at 30 but NOT at 87 when the control side (85/86) is energized, the relay contacts are bad.
    • Alternative: Carefully plug the relay back in. Ignition ON. Back-probe terminal 87 wire using a thin, stiff wire or special back-probe pins connected to DMM positive probe. Negative probe to ground. Should show +12V during prime/cranking if relay is good.

Replacing the Fuel Pump Relay in Your 1999 GS300

If testing confirms a faulty relay:

  1. Purchase Replacement:
    • Buy a quality relay with the same pin configuration and specs. Use the numbers listed earlier (TYCO V23134-B2-X044, Bosch 0 332 332 450 are extremely common equivalents) or ask for the specific fuel pump relay for a '99 GS300. OEM Denso part is ideal but good quality brands like Bosch are reliable.
    • Avoid the cheapest possible options.
  2. Prepare: Ignition OFF. Battery Negative terminal still disconnected.
  3. Remove Old Relay: Locate the relay socket in the passenger fuse box. Firmly grasp the old relay and pull it straight out. Don't twist or pry.
  4. Install New Relay: Orient the new relay so the terminal blades match the slots in the socket. Align it carefully and press it firmly straight down until it seats completely. You should feel it click into place. Make sure it's inserted correctly – forcing it can damage the terminals.
  5. Reassemble: Reattach the fuse box cover. Reinstall the passenger footwell kick panel: align the clips and press firmly into place around the edges. If screws were removed, reinstall them.
  6. Reconnect Battery: Reconnect the negative battery terminal and tighten the clamp nut securely.
  7. Test: Turn ignition to ON. You should hear the fuel pump prime for a few seconds. Attempt to start the engine. Verify normal operation.

Beyond the Relay: Related Components to Check

If replacing the relay did NOT fix the issue, the problem lies elsewhere in the fuel delivery system:

  1. EFI Fuse: Located in the main under-hood fuse box. This supplies high-current power to Terminal 30 of the fuel pump relay. A blown EFI fuse causes the exact same symptoms as a bad relay. Find it using the under-hood diagram, inspect the metal strip inside. Replace with same amperage fuse (typically 15A or 20A on GS300, check diagram!) if blown. Important: A blown EFI fuse often indicates a short circuit downstream, possibly at the fuel pump or wiring harness. Simply replacing the fuse might blow again if the underlying cause isn't fixed.
  2. Fuel Pump: Located inside the fuel tank. Can fail due to wear, contamination, or electrical failure. Requires testing voltage at the pump connector (back near the tank) or measuring fuel pressure at the fuel rail test port (requires a gauge). Replacement involves accessing the pump through the rear seat or trunk floor panel – a more involved job.
  3. Fuel Pump Wiring & Connectors: Wiring harnesses can become damaged, chafed, or corroded, especially:
    • The power wire from the relay (Terminal 87) to the fuel pump.
    • The ground wire for the fuel pump (often near the pump itself under the car, or near the tank).
    • The wiring/connections for the relay control circuit (Terminals 85/86), potentially back to the ECU.
  4. ECU (Engine Control Unit): While less common than a relay or fuse, the ECU could fail to send the ground signal to Terminal 85, preventing the relay from activating. Diagnosing this usually requires deeper electrical knowledge and checking for the signal directly at the ECU connectors.
  5. Ignition Switch: Faults in the ignition switch could interrupt the power sent to Terminal 86 or prevent the ECU from waking up and sending the ground signal. Symptoms might be more widespread than just fuel pump issues.
  6. Fuel Filter: While not electrical, a severely clogged fuel filter can mimic low pressure symptoms, though the pump should still prime audibly.

Crucial Safety Precautions

  • Always Disconnect Battery: Especially when working with relays and fuses involving high current circuits like the fuel pump. Prevents shorts, sparks, and potential electrical damage.
  • No Smoking/Open Flames: You are working on a fuel system component. Gasoline fumes are present. Avoid sparks near the fuel tank or when handling potentially shorted wiring.
  • Handle Relays Carefully: Pull straight out; plug straight in. Bent terminals cause poor connections.
  • Use Correct Tools: Don't force trim panels. Use appropriate screwdrivers/sockets. Back-probe carefully to avoid damaging wires/connectors.
  • Understand Limits: If testing points beyond a simple relay swap/fuse check, or you lack confidence/tools, consult a professional mechanic. Fuel pump issues can have multiple causes.

Practical Troubleshooting Scenarios

  • Scenario 1: No Prime Sound When Key Turned On

    • Step 1: Check EFI fuse under the hood (engine bay fuse box).
    • Step 2: If fuse good, check fuel pump relay in passenger footwell using swap test.
    • Step 3: If relay swap doesn't fix it, confirm power at Terminal 30 of relay socket.
    • Step 4: If power at 30, check for power at Terminal 86 (ignition ON) and ground path at Terminal 85 (ignition ON). Requires test light/DMM.

  • Scenario 2: Car Cranks But Won't Start - Hear Prime Sound

    • This reduces the likelihood of relay/fuse being the main issue but doesn't rule them out completely (failing pump could overdraw fuse/relay). Focus shifts more towards:
      • Fuel pump itself (can run but not build pressure).
      • Fuel pressure regulator.
      • Clogged fuel filter.
      • Major engine sensors failing (crank/cam position) preventing injector pulse/spark even though pump runs.
      • Ignition issues. However, always verify relay function per tests above.

Conclusion: Your Key to Fuel System Power

The fuel pump relay in your 1999 Lexus GS300 is a critical, yet surprisingly simple component hidden in the passenger footwell fuse box behind the kick panel. Knowing its exact location empowers you to start diagnosing common fuel delivery problems, specifically a "cranks but won't start" condition with no fuel pump prime sound. Remember the process:

  1. Locate it: Passenger footwell fuse/relay box, accessible after removing the lower kick panel.
  2. Identify it: Use the diagram on the box cover ("FUEL PUMP" label) and look for a standard black ISO micro relay.
  3. Test it: Don't guess! Perform the swap test first. Use a multimeter/test light to confirm power flow if needed. Check the vital EFI fuse under the hood!
  4. Replace it correctly: If faulty, use a quality equivalent relay and install it firmly and straight into the socket.
  5. Look further if necessary: If the relay and fuse are good, the problem lies deeper with the pump, wiring, connectors, ground, or potentially the ECU or ignition switch.

Equipped with this knowledge, you can confidently tackle the core electrical switch controlling fuel delivery in your classic Lexus GS300. Keep this guide handy for a smooth diagnosis and repair.

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