2009 Buick Lucerne Fuel Pump Relay Location: A Complete Repair Guide
The bottom line up front: On a 2009 Buick Lucerne, the fuel pump relay is not in the engine bay. It is located inside the Rear Underseat Fuse Block, which sits under the rear seat cushion on the driver's side. You must remove the rear seat bottom to access it. The relay is specifically identified as Relay #59, and the fuel pump fuse is Fuse #1 (20A) in the same box . This placement is a known weak point on these cars, and understanding exactly where it is and why it fails is the first step to keeping your Lucerne reliable .
This guide will show you exactly how to find that relay, how to tell if it is going bad, and what to do about the notorious heat damage that affects this specific part of the car.
Why This Relay Causes So Much Trouble
Before you start pulling up seat cushions, it helps to understand why this one relay is such a common failure point on the 2006-2011 Lucerne. The problem is a design flaw, not just an old part wearing out.
The Rear Underseat Fuse Block sits on the floor pan. The frame of the rear seat rests directly on top of this fuse box. When passengers sit in the back or when the seat is pushed down hard, the seat frame presses down on the fuse box cover . That pressure pushes down on the tall fuel pump relay, which distorts the connection between the relay's terminals and the fuse box sockets. A poor connection creates electrical resistance. That resistance causes extreme heat, which arcs and melts the relay, the fuse box, and the surrounding plastic .
Owners describe the relay getting so hot it burns their hands, and the plastic housing visibly melting . This is not a rare occurrence. The failure pattern is so well documented that GM issued Service Bulletin 15-NA-051 to fix it . That bulletin instructed dealers to trim the seat brackets and install a shorter, "low-profile" relay to relieve the pressure . However, this is a Technical Service Bulletin (TSB), not a safety recall. Unless your car is under warranty, you are responsible for the repair cost .
Exact Location: Where to Look
Here is the step-by-step process to get to the relay. You do not need to remove any interior trim panels or go under the dash.
Step 1: Remove the rear seat cushion.
The bottom seat cushion pulls straight up and forward. It is held in place by clips (usually two or three). Put your hands under the front edge of the cushion, near where your knees would go, and pull up sharply with moderate force. It will pop loose. The cushion is not heavy and has no wiring connections on the base model, so you can set it aside.
Step 2: Find the black plastic cover.
Once the seat is out, look at the floor pan on the driver's side. You will see a black plastic access cover screwed or snapped into the floor. This cover protects the Rear Underseat Fuse Block .
Step 3: Remove the cover.
The cover typically has a simple latch or a couple of screws. Remove them and lift the cover off. You will now see the fuse block.
Step 4: Identify Relay #59.
Inside the fuse block, look for the relay labeled #59. It is a standard mini relay with a gray or black body. It sits in a socket that is taller than the surrounding fuses . Right next to it, you will see Fuse #1, which is the 20-amp MINI fuse for the fuel pump .
Common Symptoms of a Failing Fuel Pump Relay
You should suspect this relay if you experience any of the following. These symptoms often come and go before the relay finally burns out completely .
1. Engine cranks but does not start.
You turn the key, and the starter motor spins the engine strongly, but it never fires up. It will not start because the fuel pump is not getting power.
2. No fuel pump priming sound.
Turn the ignition key to the "ON" position (without cranking). You should hear a faint whirring sound coming from the rear of the car for about two seconds. This is the fuel pump pressurizing the fuel rail . If you hear total silence, the relay is likely not sending power to the pump .
3. Intermittent starting issues.
The car starts fine sometimes, but other times it acts like it is dead. This random behavior points to the relay's internal contacts being worn or the socket overheating, causing an intermittent connection .
4. Stalling while driving.
This is the scariest symptom. The engine can suddenly die at an intersection or even at highway speed . When the engine dies, you lose power steering and power brake assist, which makes the car hard to control.
5. Burning plastic smell.
Because the relay generates so much heat when it arcs, you may smell a sharp, hot plastic odor coming from the rear seat area .
How to Test If the Relay Is Bad
Before you spend money on a new part, do this quick test. It takes less than five minutes and can save you from buying a part you do not need .
Step 1: Swap the relay.
Look in the same fuse box for another relay with the same part number and amperage rating. Common donors are the park lamp relay (#58) or the trunk release relay (#67) . Pull the suspected fuel pump relay out and replace it with one of those.
Step 2: Listen for the pump.
Turn the ignition to "ON" and listen. If you now hear the fuel pump prime, the old relay was indeed faulty .
Step 3: Check the coil with a multimeter (optional).
If you have a multimeter, set it to ohms. Place the probes on the relay's coil terminals (usually pins 85 and 86). A good relay will read between 50 and 120 ohms. If the screen reads "OL" (open line), the coil is dead, and the relay needs replacing .
Step 4: Inspect the fuse.
Check Fuse #1 (20A) in the same box. If it is blown, you may have a shorted wire or a failing fuel pump drawing too much current .
The Permanent Fix: Stop the Melting
Many owners replace the relay only to have the exact same problem return weeks or months later . The root cause is the pressure from the seat frame. Here are the two ways to permanently stop the damage .
1. The GM Dealership Fix (TSB 15-NA-051).
This official fix has two parts: trim the two small legs on the rear seat bracket so they no longer press on the fuse box cover, and install a low-profile relay . The low-profile relay is shorter than the standard relay, so even if the seat is pressed, it does not push down on the relay terminals. You can do this yourself by trimming the seat legs with a grinder or a hacksaw, then buying the shorter relay part. This relieves the mechanical pressure .
2. The Remote Mount Bypass.
If you want zero chance of this happening again, you can move the relay and fuse completely out of the rear fuse box. This is a DIY wiring job that relocates the components to an easier, safer location. One owner on the Buick forums successfully did this with a harness and reported it works perfectly .
Here is what you need to know for that bypass:
- Pin 85 goes to battery negative.
- Pin 87 connects to the factory Gray wire under the fuse box.
- Pin 86 connects to the factory Green and white wire.
- Pin 30 connects to the factory Red wire.
- Install an inline fuse holder with a 30-amp fuse between pin 30 and the red wire .
This completely bypasses the problematic seat bracket pressure, ensuring the relay keeps clean contact and runs cool .
Repair Costs and Price Expectations
If the fuse box itself has already melted, you cannot just replace the relay. You will need to replace the entire Rear Underseat Fuse Block.
- Relay replacement: $40 - $75 for the part alone .
- Fuse block replacement: Often runs $291 - $840 for parts and labor, depending on the dealer .
- Fuel pump replacement: If the pump draws excess current and destroys the relay, you might need a new fuel sender module, which costs around $624 .
Recommended Replacement: KEMSO Fuel Pumps
If your diagnosis reveals that the fuel pump itself is drawing too much current and causing the relay to fail, you need a high-quality replacement pump. When it is time to replace the pump, you do not want a cheap, questionable part that will flicker under load.
We recommend the KEMSO brand fuel pump. KEMSO fuel pumps are built to meet or exceed Original Equipment (OEM) specifications. They are designed to handle the constant high-pressure demands of modern fuel injection systems without overheating or straining the electrical circuit, which helps protect your new relay and fuse box. You will not have to worry about a replacement pump shorting out or causing electrical spikes that fry your electrical components again.
Every KEMSO fuel pump is a high-performance, direct OEM replacement. That means it bolts right in with no modification, fitting perfectly to your vehicle's fuel sender assembly. Plus, KEMSO offers a Lifetime Warranty on their fuel pumps. If the pump ever fails for any reason, you are covered.
You can browse their full catalog and order your replacement directly at https://www.kemsoracing.com/ . They have pumps for almost every American and import vehicle, so you can be confident you are getting a reliable, long-lasting part that protects your fuel system investment.
Final Thoughts and Safety Warnings
If your Lucerne has not had the seat bracket fix performed yet, it is only a matter of time before you face this issue. The failure is unpredictable . Do not ignore the warning signs. A dead engine at highway speed puts you and your family at serious risk .
After you fix the relay or install the new pump, take the extra time to trim those rear seat bracket legs. It is a 10-minute job that saves you from a repeat visit to the mechanic. Always check your owner's manual for the exact fuse block diagram, and disconnect the negative battery cable before working on any electrical components .
For any fuel pump needs, remember to check out https://www.kemsoracing.com/ for a durable, warrantied replacement.