1999 Acura TL Fuel Pump Relay Location: Your Definitive Guide and Troubleshooting Companion

Confidently locate, test, and replace the fuel pump relay in your 1999 Acura TL with this step-by-step expert guide. Struggling with a car that cranks but won't start? A failing fuel pump relay is a frequent culprit. Knowing precisely where it is saves time, money, and frustration. The fuel pump relay (Honda part number 39400-S84-A01 or equivalent aftermarket) in your 1999 Acura TL is located inside the interior under-dash fuse/relay box, specifically positioned in Slot Number 4. Access requires removing the driver's side lower dashboard panel.

Understanding the Fuel Pump Relay's Critical Role

Before diving into the physical location, grasp why finding this relay matters. The fuel pump relay is an electronically controlled switch. It acts as the gatekeeper for the electrical power supplying your car's electric fuel pump. When you turn the ignition key to the "ON" (II) position, the Powertrain Control Module (PCM, or ECU) sends a brief signal to energize the fuel pump relay for 2 seconds. This primes the fuel system. If the engine then cranks (indicating it might start), the PCM maintains the relay's energized state. When the relay clicks closed, it completes the high-current circuit, allowing battery voltage (12V+) to flow directly to the fuel pump motor located inside the fuel tank. The pump pressurizes the fuel injectors so they can spray fuel into the engine cylinders. If this relay fails – gets stuck open, clicks erratically, or stops clicking altogether – power never reaches the fuel pump. Result: Your Acura TL cranks normally but refuses to start due to lack of fuel. Symptoms mimic a bad fuel pump, fuel pump fuse, or ignition problem, making accurate diagnosis essential.

Essential Safety Preparations and Tools

  1. Work Area: Park on level ground, apply the parking brake firmly, and shift into Park (Automatic) or Neutral with brake applied (Manual). Engage wheel chocks if possible.
  2. Battery Safety: Always disconnect the negative (-) terminal of the battery before working on electrical components. This prevents accidental short circuits that could cause damage, fire, or unexpected component activation (like the starter engaging). Use a 10mm wrench. Isolate the negative cable away from the terminal.
  3. Tools & Supplies:
    • Phillips screwdriver (#2 typically)
    • Flashlight or work light
    • Needle-nose pliers (optional, helpful for relay removal)
    • Multimeter (for testing voltage and relay function - recommended for thorough diagnosis)
    • 12V test light (alternative simpler check tool)
    • Replacement relay (Honda 39400-S84-A01 or confirmed equivalent aftermarket like Standard Motors RY-134, Bosch 0332019110). Ensure it matches physically and the terminal pinout diagram (found on the relay body or box).
    • A helper (Optional, useful for activating ignition/test sequences while you monitor under the dash).

Detailed Access Procedure: Step-by-Step

The target lies behind the driver's side lower dashboard panel, often called the "knee bolster" panel.

  1. Locate the Panel: Sit in the driver's seat and look down towards your feet. Directly above your feet and below the steering column is a large, slightly textured plastic panel that curves under the dashboard. This panel is secured by several screws.
  2. Identify Screws: Typically, you will find:
    • One or two screws positioned vertically near the hood release lever.
    • One or two screws along the bottom edge of the panel, facing the driver's feet.
    • Sometimes a screw or two within the driver's door jamb area on the side edge of the panel. Check carefully. Look also for small circular covers hiding screws near the lower edge or corners.
  3. Remove Screws: Use your Phillips screwdriver to remove all screws securing this lower panel. Place screws somewhere safe.
  4. Detach the Panel: Once all screws are removed, gently grasp the panel (often at the top near the instrument cluster area or around the hood release lever) and carefully pull it towards you. It is secured by plastic clips/clamps besides the screws. Pull firmly but evenly to avoid breaking clips. There might be wiring harnesses clipped to the back of the panel (like the hood release cable holder, possibly a diagnostic connector, or light wiring). If encountered, carefully unclip any harness holders.
  5. Expose the Fuse/Relay Box: With the panel removed, look up and slightly towards the center of the car (inboard direction). You will see a dark-colored, rectangular plastic box mounted to the inner metal structure of the dashboard frame. This is the Interior Under-Dash Fuse/Relay Box.
  6. Identify the Cover: This box has a front cover. Locate the small plastic tabs on the sides or top/bottom. Squeeze the tabs inward and gently pry the cover off to reveal the fuses and relays inside. Keep the cover safe.

Locating the Fuel Pump Relay (Slot #4)

With the fuse/relay box cover removed, examine the relays inside. They will have clear labels either molded into the plastic near their sockets or printed on a diagram attached to the back of the cover you just removed.

  1. Find Slot #4: Search for the slot marked "4". In the 1999 Acura TL, this slot is designated for the fuel pump relay. It's one of several similar-looking cube-shaped black relays within the box.
  2. Confirm Relay Labeling: The relay itself will likely have printing on its side. Look for identifiers like "FUEL PUMP," "P/G," (Primary/Secondary), or simply the part number "39400-S84-A01". Honda often uses "P/G" labeling for this primary relay circuit. The diagram on the removed cover is the most authoritative source. Verify you have Slot #4.
  3. Compare and Contrast: Common other relays in this box include MAIN RELAY (Slot #1), FAN CONTROL RELAY (Slot #2 - often labelled "RAD FAN"), DEFOGGER RELAY (Slot #3 - may say "FR DEF"), and some fuse sockets. Distinguish Slot #4 from these.

Visual Identification (Understanding Relay Appearance)

  • Shape & Size: All standard relays in this box share the same form factor: A small black cube approximately 1 inch (25mm) in each dimension.
  • Terminals: The bottom has blade terminals designed to plug into the socket.
  • Label: On top or the side, printed labeling usually includes:
    • The terminal diagram (crucial for testing): Usually shows numbers like "85", "86", "87", "30", "87a". The fuel pump relay typically uses only four: 85, 86 (coil control side), 30 (Power Input), 87 (Output to Pump).
    • Specifications (12V, DC).
    • Manufacturer part numbers or symbols.
    • Functional label like "P/G" or "FUEL PUMP" (but not always clearly).
  • Slot Label Override: The label molded into the box plastic next to the relay socket ("4") and the diagram on the cover are the most reliable indicators for function in Slot #4. Do not rely solely on the printing on the relay itself, as relays can get swapped during previous repairs.

Verifying Functionality: Is the Relay the Problem?

Do not replace parts blindly. Confirming a faulty relay prevents unnecessary costs.

Method 1: The "Click Test" (Simplest)

  1. Have helper sit in driver's seat.
  2. Reconnect the battery negative terminal.
  3. Stand outside driver's door, door open, kneel down near opening.
  4. Instruct helper to turn ignition key to the ON (II) position (don't crank engine). Listen closely under the dash for a distinct "click" sound coming from the relay box area. You should hear a solid "click" within 1-2 seconds of turning to ON. This is the relay energizing (closing).
  5. Helper should leave key ON for 10-15 seconds. Relay should stay energized (click stays closed). They then turn key back to OFF (O). Listen for another distinct click as the relay de-energizes (opens). No click, or a weak/erratic click, suggests a relay or control circuit problem. If you hear a click but suspect pump isn't running, proceed to voltage tests.

Method 2: Voltage Testing with Multimeter (Most Accurate)

  1. Disconnect battery negative terminal again.
  2. Remove the Fuel Pump Relay from its socket (Slot #4) using needle-nose pliers if necessary. Pull straight out.
  3. Examine the socket cavity. You will see 4 or 5 blade receptacles. Identify their terminal numbers. These are usually molded into the plastic near each slot: 85, 86, 87, 30.
    • 85: Control coil ground (often powered during crank/run).
    • 86: Control coil +12V supply (from ignition switch/PCM trigger).
    • 87: Relay Output to Fuel Pump (+12V).
    • 30: Constant +12V Power Input from fuse.
  4. Reconnect battery negative terminal.
  5. Set multimeter to DC Volts (20V range).
  6. Test 1: Check Power Input (Terminal 30): Place multimeter black probe on a solid ground point (bare metal bolt/screw). Place red probe into the socket slot corresponding to Terminal 30. With key OFF, you should see ~12V battery voltage. If not, check the FUEL PUMP fuse in the main engine bay fuse box (usually labeled "FUEL PUMP").
  7. Test 2: Check Control Signal (Terminals 85 & 86):
    • Place multimeter red probe on socket Terminal 86. Black probe on ground.
    • Turn ignition key to ON (II). You should see a brief pulse of ~12V that lasts ~2 seconds, then drops to 0V. This is the PCM priming signal.
    • Now, instruct helper to turn the key to START (crank position). While cranking (engine turning over), the voltage at Term 86 should jump back to ~12V and stay there as long as the key is held in START or if the engine starts and key returns to ON (II). If voltage at 86 is absent during crank/run, the problem lies in the control circuit (ignition switch, wiring, PCM signal).
    • Place multimeter red probe on socket Terminal 85. Black probe on ground.
    • With key ON during crank/run, you should see continuity (~0V voltage if testing across 85-ground, OR measure resistance later). Terminal 85 is typically grounded internally by the PCM when active. Expect ~12V across terminals 85 & 86 (coil terminals) when the control circuit is activated during crank/run.
  8. Test 3: Check Output Socket (Terminal 87): This tests the circuit to the pump using the relay socket. Place multimeter red probe into socket Terminal 87. Black probe on ground. Have helper turn key to START (Crank). You should measure ~12V battery voltage at Terminal 87 only while the key is held in the START position. If voltage is present here during cranking but the pump isn't running, the problem is between this socket and the pump (wiring, harness connector, pump itself, or ground). If voltage is absent here during cranking despite good inputs at 30, 85, and 86, AND the relay has been confirmed good (see swap test below), the socket or wiring between 30 and 87 internally is bad (rare).

Method 3: Swap Test (Substitution)

  1. Locate another identical relay in one of the adjacent slots (e.g., the Radiator Fan Relay in Slot #2). Confirm it's the same part number/shape/terminal layout. Compare the diagrams on the relays carefully.
  2. Swap the suspected fuel pump relay from Slot #4 with this known good relay from Slot #2.
  3. Perform the "Click Test" (Method 1) with the ignition key. If you now hear a strong click from the FUEL PUMP position (Slot #4) using the relay taken from Slot #2, the original relay was bad. If the no-click symptom persists in Slot #4, the problem is likely the control circuit or socket.
  4. Verify the swapped relay hasn't caused the fan to malfunction before driving the car long term (a brief test is ok). Replace both relays if the swap identified a bad one.

Relay Removal and Replacement

  1. Verify Failure: Confirm through one of the tests above that the relay needs replacement.
  2. Purchase Correct Part: Obtain Honda 39400-S84-A01 or guaranteed equivalent aftermarket relay.
  3. Disconnect Battery: Disconnect negative terminal.
  4. Access & Remove Panel: Follow steps earlier to remove the driver's lower dash panel and fuse box cover.
  5. Extract Old Relay: Firmly grasp the relay and pull it straight out from its socket. Use pliers gently if needed.
  6. Install New Relay: Orient the new relay so its blade terminal pattern matches the socket. Align it carefully (check if terminals are offset) and push it firmly and evenly straight down into the socket. You should feel it click or seat securely.
  7. Reassemble: Replace the fuse box cover securely, aligning tabs. Reattach the driver's lower dash panel. Install all screws removed earlier in their original locations. Tighten snugly but avoid over-tightening plastic threads.
  8. Reconnect Battery: Reconnect the battery negative terminal.
  9. Test: Turn ignition to ON - listen for relay click. Start the engine - it should crank and start normally if the relay was the culprit.

Troubleshooting Guide: Beyond the Relay Location

If accessing the relay location and performing the tests doesn't resolve the no-start issue, here's a systematic approach:

  1. Confirm Fuel Pump Fuse: Check the 15A FUEL PUMP fuse in the engine bay fuse box (under the hood). Pull it out and inspect the element visually for a break. Test for continuity with a multimeter. Replace if blown. Investigate why it blew.
  2. Inspect Wiring: Visually examine the wiring harness connecting to the fuse/relay box and traces running along the driver's side kick panel down towards the rear of the car. Look for any obvious damage, chafing, corrosion, or loose connections, especially at plug connectors.
  3. Listen for Pump Priming: When turning key to ON, can you hear the fuel pump hum/whirr for 2 seconds? Sound comes from the rear, near the fuel tank. If silent, power isn't getting to it (fuse, relay, wiring).
  4. Check Fuel Pressure: Needs a pressure gauge. Tap into the Schrader valve on the fuel rail under the hood. Should get ~45-50 PSI prime pressure, rising to ~50-55 PSI during cranking/running. Low or no pressure indicates supply problem upstream of injectors.
  5. Pump Power Direct Test: Bypass relay circuit. With battery connected and key ON, carefully supply +12V directly to the fuel pump connector (usually accessible near the fuel tank under the car, sometimes behind rear seat interior panels - consult specific TL access guide). Use fused jumper wires or fused power source and identify the correct power wire (often solid BLK/YEL or YEL/BLK - check wiring diagram for certainty; disconnect plug and use multimeter to identify power pin with ignition ON during crank sequence). If pump runs with direct power, the problem is in the control circuit (relay, fuse, wiring harness, PCM signal). WARNING: Handle fuel system connections only in a well-ventilated area with no ignition sources. High fuel pressure present.
  6. Check Grounds: Bad grounds can disrupt the circuit. Check the relay control ground path. Verify known good grounds at the pump end. Clean any corroded ground connections.
  7. Scan for Codes: Use an OBD-II scanner. While fuel pump relay failure doesn't always set a code, you might see P0627 (Fuel Pump "A" Control Circuit/Open) or codes related to sensor power (like P1630/P1631 EGR/Power Circuit) if the main relay is also involved, or misfire/cranks-no-start codes caused by no fuel. Check PCM for communication issues. Look for stored history codes related to fuel or electrical systems.
  8. Ignition Switch: Faulty ignition switches can prevent signals reaching the PCM or the relay control circuit.
  9. PCM Signal Fault: Rare, but possible. Requires diagnostic capability to probe PCM outputs or interface through diagnostic connector for active tests commanding relay activation.
  10. Fuel Pump Failure: If power is confirmed reaching the fuel pump connector during cranking and grounds are good, the fuel pump itself is likely faulty. Requires pump assembly replacement (access via fuel tank, major procedure).

Maintenance Tips and Longevity

  • Use Quality Relays: OEM or reputable brand relays provide consistent performance.
  • Address Electrical Gremlins: Solve wiring shorts or faulty grounds promptly. Intermittent power surges strain relays.
  • Avoid Moisture: Ensure fuse box covers and seals are intact. Significant moisture ingress can corrode relay contacts.
  • Recognize Early Signs: Intermittent no-start events, especially when warm, sometimes preceded by a faint fuel pump relay buzz or multiple weak clicks instead of one solid click. Act proactively.

FAQs

  • Q: Does a bad fuel pump relay blow the fuse?
    • A: Sometimes, but not always. A relay with contacts welded shut or severe internal shorts could blow the fuel pump fuse. However, a simple open circuit (no click) or weak operation typically does not blow fuses. A blown fuse often points to a downstream problem like a shorted fuel pump or damaged wiring harness.
  • Q: How much does it cost to replace a fuel pump relay on a 1999 Acura TL?
    • A: DIY Cost: 35 USD for a quality aftermarket relay (less for basic, more for premium/OEM). Professional Shop: Expect 120 USD. The high cost is primarily labor for accessing the fuse box; the relay itself is cheap. This is why DIY is strongly encouraged.
  • Q: How long should a fuel pump relay last?
    • A: They are generally reliable and should last the vehicle's lifetime. Premature failure (50,000-150,000 miles) can occur due to excessive electrical load surges (rare), extreme heat cycles under the dash, internal manufacturing defects, or contamination/corrosion from moisture. Age alone is less a factor than usage/cycles.
  • Q: Can a bad fuel pump relay cause stalling?
    • A: Yes, absolutely. If a relay becomes intermittently faulty – clicking on and off erratically while driving – power to the fuel pump will be cut sporadically. This causes the engine to stall abruptly without warning. Once stalled, it may crank but not restart until the relay decides to work again, possibly after cooling off.
  • Q: Where is the fuel pump itself located?
    • A: The electric fuel pump is located inside the fuel tank. Access requires lowering the fuel tank or gaining entry through an access panel underneath the rear seat. It's a significantly more complex procedure than replacing the relay.

Conclusion

Knowing the precise location of the fuel pump relay – Slot #4 in the interior under-dash fuse/relay box – empowers 1999 Acura TL owners to tackle a common cause of frustrating "cranks but won't start" problems. By methodically accessing the relay, testing it using sound, voltage, or substitution techniques, and replacing it if faulty, you can often restore reliable engine starts quickly and affordably. Remember safety precautions, especially battery disconnection. Understanding the diagnostics pathway outlined here also helps pinpoint if the issue lies elsewhere in the fuel delivery or electrical system. Armed with this comprehensive guide, you possess the practical knowledge to solve this frequent Acura TL malfunction confidently.

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