2009 GMC Acadia Fuel Pump Relay Location: Your Direct Answer & Full Guide

The fuel pump relay on a 2009 GMC Acadia is located in the Underhood Electrical Center (UEC), specifically within the main fuse box positioned near the driver's side strut tower in the engine compartment. Reaching it requires lifting the hood and identifying the large, black plastic box.

Knowing where the fuel pump relay is sits at the heart of troubleshooting a huge range of starting and running problems on your 2009 GMC Acadia. A failed relay is a common culprit when your engine cranks but refuses to start. Reaching the relay is straightforward, making replacement a relatively simple and inexpensive DIY task compared to many automotive repairs.

Understanding the Underhood Electrical Center (UEC)
The UEC is the primary hub for electrical distribution in your Acadia's engine bay. It houses the majority of high-current fuses and vital system relays, including the one controlling the fuel pump. On the 2009 Acadia, you'll find this rectangular black box secured firmly near the driver's side strut tower – the shock absorber mounting point closest to the windshield on your left as you stand facing the engine bay. It's generally larger than other secondary fuse boxes you might find elsewhere.

Precise Relay Location Within the UEC Box

  1. Locate the Box: Open the hood. Look for the large, rectangular black plastic cover, typically labeled "Underhood Electrical Center" or similar. It will be positioned towards the rear of the engine bay on the driver's side, adjacent to the windshield washer fluid reservoir and behind the air intake ducting in many cases.
  2. Access the Relays: To get to the relays, you must remove the cover. This usually involves pressing in retaining clips at each corner or along the sides and lifting the cover upwards. Set the cover aside safely.
  3. Identify the Relay: Inside the box, you'll see an array of fuses (smaller, often transparent or colored plastic) and larger cube-shaped components – these are the relays. The fuel pump relay is typically identified by:
    • Diagram: Look for a fuse/relay layout diagram printed inside the UEC cover or molded into the plastic body of the fuse box itself. This diagram is your definitive guide and will clearly mark the location for the "Fuel Pump" relay.
    • Labeling: Relay slots are often labeled adjacent to the position. Scan for "FUEL PUMP," "F/P," "FP," or similar labeling stamped into the plastic next to the relay socket.
    • Position: While layouts can vary slightly, the fuel pump relay is commonly found in the front row or towards the center of the box relative to the engine firewall.

How to Visually Confirm You Have the Fuel Pump Relay
The relay itself is a small, square or cube-shaped, black plastic component with either 4 or 5 metal blade terminals on the bottom. It plugs into its designated socket in the fuse box. Crucial points:

  • Color: While sometimes varying (brown, gray), black is common. Don't rely solely on color.
  • Shape: Standard "cube" micro-relay shape, roughly 1 inch square.
  • Terminals: Look for the specific terminal layout matching the socket labeled for the fuel pump in your diagram.
  • Testing Check: Before assuming it's faulty, testing (or swapping with an identical relay like the A/C clutch relay) is recommended. See the section below.

Why the Relay Matters: The Fuel Pump Circuit Simplified
The fuel pump relay acts as a heavy-duty electrical switch controlled by the Powertrain Control Module (PCM – your engine's main computer). Here’s the sequence:

  1. Ignition Key Turned to "RUN": The PCM receives a signal.
  2. PCM Activation: The PCM sends a small ground signal to the coil inside the fuel pump relay.
  3. Relay Closes: This energizes the coil, magnetically closing internal contact points inside the relay.
  4. Power to Pump: Closing these contacts connects the high-amperage battery power (via a fuse) through the relay directly to the electric fuel pump in the tank.
  5. Pump Operation: The fuel pump pressurizes the fuel line, supplying the injectors so the engine can start and run.
    If the relay fails to close or its contacts are burned out, the vital power signal never reaches the fuel pump. Result: no fuel pressure, no start.

Symptoms of a Failing Fuel Pump Relay
While a dead relay is obvious (no start), symptoms of a failing relay can be intermittent:

  • Crank, No Start: The most definitive symptom. Engine cranks normally but does not fire. You may or may not hear the brief (2-second) fuel pump prime sound when you turn the key to "RUN" before cranking.
  • Intermittent No-Start: Starts fine sometimes, other times it cranks forever without starting. Might start after sitting for a while.
  • Engine Stalling While Driving: The relay contacts can momentarily lose connection, cutting power to the pump and stopping the engine abruptly without warning, potentially dangerous.
  • Loss of Prime Sound: You no longer hear the characteristic "whir" or "hum" from the rear of the vehicle for 1-2 seconds when turning the key to "ON" or "RUN."
  • Intermittent Power Loss: Similar to stalling, but perhaps just a momentary cut-out while driving.
  • Overcoming Stall/Restart: Car might stall and then restart immediately or after a few minutes. This "cooldown" period can be characteristic of a failing relay when it heats up.

Testing the Fuel Pump Relay Before Replacement
Avoid unnecessary costs by testing:

  1. Swap Test: Find another identical relay in the fuse box. A common choice is the Air Conditioning (A/C) Clutch relay. Crucial: Compare the diagrams/labels to ensure they are the exact same relay type (micro-relay, same pin configuration). Swap their positions. If the "crank no start" symptom remains, the relay is probably not the problem. If the symptom changes (e.g., your A/C stops engaging but the car starts!), then the original relay is faulty. This is the simplest test.
  2. Listen for Pump: With key to "ON" (not start), have a helper carefully listen near the fuel filler door. You should hear a distinct buzzing/whining for about 2 seconds. If you hear it, the relay triggered the pump. If you hear nothing and you have a crank-no-start condition, the relay (or its fuse/power source, or pump) is suspect.
  3. Visual Inspection: Remove the relay. Look for signs of overheating: melted plastic casing, discolored or scorched terminals, or a burnt smell.
  4. Multimeter Test (Advanced): Requires tools and electrical knowledge.
    • Resistance: Test the coil between terminals identified as "coil" in the relay diagram (often terminals 85 & 86). Should show continuity/resistance (e.g., 60-100 Ohms). An open circuit (infinite Ohms) means the coil is bad.
    • Contacts: Apply 12V across the coil terminals (85+86). Listen/feel for an audible "click." Then test continuity between the high-power switched terminals (often 30 & 87). Should show continuity (~0 Ohms) when coil is energized.
    • Terminal Identification: Terminal 30: Constant Battery Power (via fuse). Terminal 87: Output to Fuel Pump. Terminal 85: Coil Ground. Terminal 86: Coil Power (From PCM).

Replacing the Fuel Pump Relay: Step-by-Step
Safety First: Always disconnect the negative battery cable before working on electrical components to prevent shorts, sparks, or accidental activation. Disconnect and isolate the cable.

  1. Locate: Identify the UEC near the driver's side strut tower. Remove the cover.
  2. Identify Relay: Use the diagram/label inside the cover or molded on the box to locate the exact "Fuel Pump" relay slot.
  3. Remove: Grasp the faulty relay firmly and pull it straight out of its socket. Avoid twisting.
  4. Verify Replacement: Ensure the new relay is the exact same type, shape, and terminal configuration (number and layout) as the original. Micro-Relay ISO 280 is a common standard for GM vehicles like the Acadia. Don't guess!
  5. Install: Align the new relay terminals perfectly with the socket holes. Push firmly and evenly until it seats completely. You should feel a solid connection. Forcing it indicates misalignment.
  6. Reconnect: Replace the UEC cover securely. Reconnect the negative battery cable.
  7. Test: Turn the key to "ON." You should hear the fuel pump prime for a few seconds. Then start the engine.

Crucial Caveats and Misconceptions

  • "It Must Be the Pump": While a bad pump is possible, a relay (or fuse) is far more common and always cheaper and easier to check first. Don't jump to dropping the tank!
  • Fuse Check: Always inspect the fuel pump fuse (located in the same UEC box, identified by the diagram/label). A blown fuse means there's an underlying problem causing excessive current draw (short circuit, failing pump). Simply replacing the fuse without fixing the cause will lead to it blowing again. Replace the fuse only after addressing the root cause.
  • "Dealer Only" Part: Micro-relays are standard components. You can purchase an exact match from auto parts stores (e.g., Standard Motor Products RY121, BWD R3121 – verify compatibility) or GM. Avoid universal relays unless specifically recommended for your application.
  • Relay vs. Control Module: The relay is a simple switch. Complex failure modes usually point elsewhere. "Bad PCM control" is relatively rare.
  • Resetting Issues: While you technically "reset" the fuel pump relay's last state by disconnecting the battery, this isn't a diagnostic procedure on its own. The problem will return if the relay is faulty.

What Else to Check If the Relay is Good
If the relay tests fine and the pump doesn't run:

  1. Fuel Pump Fuse: Check for continuity with a multimeter or visually inspect the metal strip inside the fuse. Replace if blown, but investigate why it blew.
  2. Fuel Pump: You'll need to diagnose the pump itself (power at pump connector, ground integrity) or listen for it priming. A "thump" test hitting the tank while someone cranks is unreliable on modern vehicles.
  3. Fuel Pump Wiring: Check for damaged wiring harnesses in the engine bay, underbody, or near the fuel tank. Look for corrosion, pinches, or rodent damage.
  4. Anti-Theft System (Passlock): Issues with the vehicle's security system can disable the fuel injectors but not the fuel pump prime cycle. If you hear the pump prime (2-second sound), Passlock is likely not causing the no-start. If you don't hear the pump, focus elsewhere first (relay, fuse, pump). Security lights flashing on the dash when cranking indicate Passlock involvement.
  5. PCM Signal: Less common, but verifying the PCM is sending the ground signal to the relay coil (Terminal 85) requires diagnostic tools or a multimeter.

Maintenance and Prevention
While relays typically fail without warning, keeping your electrical connections clean helps prevent corrosion-related issues:

  • Ensure battery terminals are clean and tight.
  • Check UEC box seals to prevent water ingress (rare but possible).
  • Consider keeping a spare micro-relay compatible with your Acadia's fuel pump and A/C clutch in the glove box. It's cheap insurance.

Locating the fuel pump relay in your 2009 GMC Acadia places the solution to a common no-start problem directly in your hands. By understanding its role, knowing exactly where to find it in the Underhood Electrical Center near the driver's strut tower, and learning simple diagnostic steps like the swap test, you can confidently resolve starting issues quickly and inexpensively. Remember the critical safety step: always disconnect the battery before any electrical work.

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