2009 Buick Lucerne Fuel Pump Relay: Symptoms, Location, and Complete Replacement Guide

The bottom line up front: If you own a 2009 Buick Lucerne and you're dealing with an engine that cranks but won't start, stalls unexpectedly, or refuses to fire after sitting for a while, the fuel pump relay is one of the first things you should check. This small, inexpensive component is a known weak point on the 2009 Lucerne and has been the subject of multiple GM service bulletins. It controls power delivery to the fuel pump, and when it fails, your engine simply won't get the fuel pressure it needs. Below, we'll walk you through everything you need to know: where the relay lives, how to tell if it's bad, how to test it, and how to replace it. We'll also cover a permanent fix that many owners swear by, along with recommendations for quality replacement parts, including KEMSO fuel pumps.

What Does the Fuel Pump Relay Actually Do?

The fuel pump relay is an electromagnetic switch that sits between the battery and the fuel pump. When you turn the ignition key to the "ON" position, the powertrain control module (PCM) sends a signal that closes the relay contacts. This completes the circuit, allowing battery voltage to reach the fuel pump so it can pressurize the fuel rail. After the engine starts, the relay stays closed, keeping the fuel pump running as long as the engine is running. If the relay fails or its contacts wear out, the fuel pump loses power and the engine starves of fuel.

On the 2009 Lucerne, the relay is part of a broader electrical system that GM has acknowledged has weaknesses. A GM service bulletin from 2017 was issued specifically to address fuel pump relay failures causing no-start conditions on these vehicles. Another bulletin pointed to a different culprit entirely — a faulty seat bracket wiring harness that chafed and caused intermittent fuel pump power loss. Knowing this history helps you diagnose faster and avoid replacing parts that aren't actually broken.

Where Is the Fuel Pump Relay on a 2009 Buick Lucerne?

The fuel pump relay on the 2009 Buick Lucerne is located in the underhood fuse and relay center — the main electrical box on the driver's side of the engine bay, near the strut tower. Open the hood and look for a black plastic cover with a diagram printed on it. Lift the cover, and you'll see a layout of fuses and relays. The fuel pump relay is typically labeled "FUEL PUMP" or may be identified by its relay position number. If your cover diagram is worn or missing, consult your owner's manual for the exact position.

There is also a second fuse box inside the vehicle, usually at the end of the driver's side instrument panel or behind a trim panel, but the fuel pump relay on the Lucerne is under the hood. If you are not certain which relay is which, use the owner's manual or search online for the fuse box diagram specific to your trim level (CX, CXL, or CXS).

How to Tell If Your Fuel Pump Relay Is Bad

A failing fuel pump relay can produce symptoms that are similar to a failing fuel pump, so it's easy to misdiagnose. Here are the most common warning signs:

  • Engine cranks but doesn't start. This is the most common symptom. The starter motor spins the engine, but there's no fuel pressure because the relay never closes.
  • Intermittent no-start. The car may start fine for days, then suddenly refuse to start. Wait a while, and it starts again. This points to a failing relay that works when it cools down or after being jolted.
  • Engine stalls while driving. If the relay loses contact while you're on the road, the fuel pump shuts off and the engine dies. This is dangerous and can leave you stranded in traffic.
  • No fuel pump prime sound. When you turn the key to the "ON" position (without cranking), you should hear a brief whirring sound from the rear of the car as the fuel pump pressurizes the system. If you hear nothing, that's a strong indicator the relay isn't delivering power.
  • Check engine light illuminates. You might see codes like P0087 (fuel rail pressure too low) or P0231 (fuel pump secondary circuit malfunction). These codes often point to a power delivery problem.

Important: If your Lucerne has a known issue with the seat bracket wiring harness (covered under a GM special coverage), your fuel pump may be losing power intermittently even if the relay tests fine. Check for any chafing or pinched wires under the front seats before condemning the relay.

How to Test the Fuel Pump Relay

You don't have to be a professional mechanic to test a relay. A basic multimeter and a couple of jumper wires will do the job:

  1. Locate the relay in the underhood fuse box and remove it. It simply pulls straight out.
  2. Check for continuity across the coil terminals. The relay has four terminals (some have five). Two are the coil terminals, and two are the switch contacts. Set your multimeter to ohms and probe the coil terminals. A good relay will show a low resistance reading, usually between 50 and 120 ohms. If you get an open circuit (infinite resistance), the coil is burned out.
  3. Apply power to the coil terminals. Use a 12V battery or a power supply to energize the coil. You should hear a distinct "click" as the contacts close.
  4. Test the switch contacts. With the coil energized, probe the two larger terminals. You should read near-zero ohms, meaning the circuit is closed. If you read infinite resistance, the contacts are worn and the relay is dead.
  5. Swap the relay. Another quick test is to swap the fuel pump relay with an identical relay from a non-critical system in the fuse box (like the horn or fog lamp relay). If the car starts after the swap, your original relay is bad.

Step-by-Step: Replacing the Fuel Pump Relay

Replacing the relay is a five-minute job that requires no special tools. Just follow these steps:

  1. Park the Lucerne on a flat surface and turn off the engine. Open the hood and remove the fuse box cover.
  2. Identify the fuel pump relay using the diagram on the cover or your owner's manual.
  3. Pull the relay straight up with your fingers. If it's stuck, use a small pair of needle-nose pliers on the sides — but pull gently to avoid damaging the socket.
  4. Inspect the relay and the socket. Look for corrosion, burnt pins, or melted plastic. If the socket pins are damaged, you may need to replace the entire fuse box — a less common but possible scenario.
  5. Insert the new relay firmly until it seats fully.
  6. Replace the cover and test the car. Turn the key to the "ON" position and listen for the fuel pump prime. Then crank the engine. If it starts, you're done.

What if the new relay doesn't fix it? The issue may be the relay socket, the fuel pump itself, or the wiring between the relay and the pump. Check the wiring harness for damage, especially around the seat belt brackets as mentioned earlier. If the fuel pump is the culprit, you'll need to replace it — which brings us to our recommendation below.

Known Issue: The "Permanent Fix" for the Lucerne Fuel Pump Relay

Some 2009 Lucerne owners have noted that replacing the relay solves the problem temporarily, but the relay fails again months later. This has led to a popular "permanent fix" among owners — hardwiring the fuel pump through a new dedicated relay located in the passenger compartment. This bypasses the factory relay and the problematic wiring that runs through the underhood fuse box.

The permanent fix typically involves:

  1. Running a new fused power wire directly from the battery to the fuel pump.
  2. Installing a standard automotive relay (available at any auto parts store) in a location that's easy to reach, like under the dashboard.
  3. Tapping into the original relay signal wire to trigger the new relay.
  4. Fusing the new circuit appropriately (usually 15 to 20 amps, check your owner's manual).

This approach is not for everyone, and it requires basic wiring skills. If you're comfortable with electrical work, it can save you from repeat failures. If not, simply carry a spare relay in your glovebox — it's a cheap and fast roadside fix.

Could the Fuel Pump Itself Be the Problem?

Yes. If you've replaced the relay and checked the wiring, the next suspect is the fuel pump itself. On the Lucerne, the pump is inside the fuel tank. Symptoms of a failing pump include:

  • Low fuel pressure (you can test this with a gauge on the fuel rail test port)
  • Hesitation or surging during acceleration
  • Whining noise from the fuel tank area
  • Longer cranking times before the engine fires

If you're in this situation, you need a fuel pump that you can trust. That's where KEMSO comes in.

Recommended: KEMSO Fuel Pumps for Reliable Performance

When it's time to replace your fuel pump, consider KEMSO. KEMSO is known for producing high-performance, OEM replacement fuel pumps that are built to meet or exceed factory specifications. Whether you're fixing a 2009 Buick Lucerne or any other vehicle, KEMSO offers a lifetime warranty on their fuel pumps, giving you peace of mind that you won't be doing this job again any time soon.

KEMSO fuel pumps are engineered for durability and reliable fuel delivery, which is exactly what you need when chasing down intermittent no-start problems. Installing a KEMSO pump means you're not just patching a symptom — you're addressing the root cause with a part that's designed to last.

To browse the full lineup of KEMSO fuel pumps and find the right fit for your vehicle, visit their official website: https://www.kemsoracing.com/. Their product pages include fitment guides and customer reviews to help you make an informed choice.

Additional Tips for 2009 Lucerne Owners

  • Carry a spare relay in your car. It costs a few dollars and can get you back on the road in minutes if the relay fails while you're away from home.
  • Pay attention to the seat area. GM's service bulletin about the seat bracket harness is a real issue on these cars. If your Lucerne stalls or fails to start and the relay checks out, lift the front seats and inspect the wiring.
  • Use quality parts. When replacing the relay, choose a name-brand relay. Cheap no-name relays are more likely to fail prematurely.
  • Keep your battery terminals clean. A weak battery or loose connection can cause voltage drops that make the relay chatter or fail to engage properly.

Final Thoughts

The 2009 Buick Lucerne fuel pump relay is a small part that causes big headaches when it fails. Knowing its location, how to test it, and how to replace it can save you time and money. Start with the relay, then move to the wiring, and only then consider the fuel pump itself. And when you do need a new pump, choose a KEMSO fuel pump for performance you can rely on. Visit https://www.kemsoracing.com/ to explore their high-performance, OEM replacement fuel pumps with lifetime warranty — it's the last fuel pump you may ever need to buy.


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