2009 Cadillac DTS Fuel Pump Relay Location: Where It Is and How to Fix It Fast
The bottom line up front: The fuel pump relay on a 2009 Cadillac DTS is located inside the rear underseat fuse block, which sits under the rear passenger seat cushion on the driver's side. This is the same fuse block that also houses the fuel pump fuse (fuse #1, 20A) and relay #59. If your DTS cranks but won’t start, the relay or its internal connections are often the culprit — and in many documented cases, the rear fuse block itself is what fails, not the pump.
Why This Location Surprises Most Owners
If you have owned older GM cars, you might expect the fuel pump relay under the hood in the engine bay fuse box. That is a reasonable guess, and some sources do say the relay can live in the underhood box. But on the 2009 Cadillac DTS, the engineering team placed the fuel pump relay in the rear electrical center — a fuse block tucked beneath the rear seat cushion. This placement makes sense because the fuel pump and the fuel tank pressure sensor wiring both run through that area, and keeping the relay close to the pump reduces wiring length. But it also means you have to remove the rear seat cushion to get to it, which catches many owners off guard.
The same rear underseat fuse block is responsible for several other circuits, including the fuel pump fuse, the canister vent solenoid, and various body control functions. That matters because a melted or failing connection inside this block can cause symptoms that look like a dead fuel pump but are actually electrical faults in the block itself.
Exactly Where the Relay Sits in the Rear Fuse Block
The rear underseat fuse block is positioned under the rear seat on the driver's side. To access it, you need to pop the rear seat cushion up with firm upward pressure — it is held in by clips and does not require any tools. Once the cushion is out of the way, you will see the fuse block.
Inside that block, look for:
1. Fuse #1 (20A) — Fuel Pump Fuse
This is the mini fuse that directly powers the fuel pump circuit. If this fuse is blown, the pump will not run at all. A blown fuse usually points to a short to ground in the pump supply wire, or an internal fault in the pump itself.
2. Relay #59 — Fuel Pump Relay
This is the main relay you asked about. It is a standard automotive relay that the Engine Control Module (ECM) uses to switch power to the fuel pump. When you turn the ignition to ON, the ECM energizes this relay for about 2 seconds to prime the fuel system — unless it sees engine rotation pulses, in which case it keeps the relay closed and the pump running.
3. Metal Traces and Internal Connections
This is the part that fails most often. Multiple owner reports describe a melted internal connection inside the rear fuse block, specifically between the fuel pump relay socket and the fuel pump fuse socket. When that trace melts, the pump loses power intermittently or completely, even though the relay and fuse themselves look fine.
How to Confirm the Relay Is the Problem (Before You Replace Anything)
Do not just throw a new relay at the car and hope for the best. The relay is cheap, but if the root cause is a melted fuse block, the new relay will burn out just like the old one. Follow this diagnostic order:
1. Listen for the pump prime.
Turn the ignition to ON (do not crank). You should hear the fuel pump run for about 2 seconds from the rear of the car. If you hear nothing, the relay may not be closing, the fuse may be open, or the block trace may be dead.
2. Check the fuel pump fuse.
Pull fuse #1 from the rear underseat block and inspect it. A blown fuse has a melted or broken metal conductor inside. If it is blown, do not simply replace it — you need to find the short. Common causes are a damaged wire shorting to the chassis, or the pump motor pulling too much current as it fails.
3. Test the relay with a test lamp.
Remove the fuel pump relay using a relay puller pliers (GM special tool J 43244 works, but needle-nose pliers can also do the job). With the ignition ON and engine OFF, probe the control circuit terminal (terminal 3) with a test lamp connected to ground. Command the relay ON and OFF using a scan tool. The lamp should turn ON and OFF with each command.
- If the lamp does not respond, the issue is an open or short in the control wire, or a faulty ECM.
- If the lamp stays on regardless of the command, you have a short to voltage or a bad ECM.
4. Check for battery voltage at the relay.
With the ignition ON, probe terminal 1 (battery positive) with a test lamp to ground. If the lamp does not light, you have an open in the battery feed circuit.
5. Bypass the relay to test the pump directly.
Connect a 15A fused jumper wire between terminal 1 (battery positive) and terminal 5 (the supply voltage circuit to the fuel pump). If the pump runs with the jumper in place, the relay or its socket is faulty. If the pump still does not run, the problem is in the pump supply wire, the pump ground, or the pump itself.
The Hidden Culprit: Melted Rear Fuse Block
Here is what makes the 2009 DTS fuel pump relay location extra tricky. In several documented owner cases, the relay was not the problem at all — the internal connections inside the rear fuse block melted.
One owner reported a 2007 DTS that would not start, with intermittent issues before complete failure. The initial diagnosis pointed to the fuel pump, but the real root cause was a melted internal trace between the fuel pump relay socket and the fuel pump fuse socket. The fix was to bypass the faulty internal trace with an external fused jumper wire.
Another 2009 DTS owner described a similar ordeal: the car stalled in traffic, the relay was burning hot, and a new relay worked briefly before stalling again. A scan tool showed code P0230, which indicates a fuel pump relay control circuit malfunction. In that case, the underlying issue was the rear fuse block itself, requiring a full replacement at a cost of about $716 including labor.
Signs your rear fuse block may be melting:
- The relay feels abnormally hot after the car runs for a few minutes
- Fuel pump operation is intermittent — the car starts sometimes, then dies
- The fuel pump fuse looks fine but the car still will not start
- You smell burning plastic near the rear seat area
If you see any of these, inspect the underside of the fuse block for discolored or melted plastic around the relay and fuse sockets. A visual inspection can save you hours of chasing the wrong part.
Step-by-Step: How to Access and Replace the Relay
Here is the full process for reaching the fuel pump relay in a 2009 Cadillac DTS:
Step 1 — Remove the rear seat cushion.
The cushion sits on two or three clips. Grab the front edge firmly and pull upward with steady pressure. It will pop out. You do not need to disconnect any wiring unless you have a power rear seat option, in which case unplug the harness first.
Step 2 — Locate the rear underseat fuse block.
Once the cushion is up, you will see a black plastic fuse block mounted to the floor pan. It is on the driver's side, under the rear seat.
Step 3 — Identify fuse #1 and relay #59.
Refer to the diagram printed on the fuse block cover, or use the layout from the 2009 DTS fuse map. Fuse #1 is the 20A fuel pump fuse. Relay #59 is the fuel pump relay.
Step 4 — Pull the relay.
Grab the relay with a relay puller or needle-nose pliers and pull straight up. Do not rock it side to side, as that can damage the socket terminals.
Step 5 — Inspect the socket.
Look inside the socket for corrosion, loose pins, or melted plastic. If the socket looks damaged, replacing the relay alone will not fix the problem — you need to repair or replace the fuse block.
Step 6 — Install the new relay.
Press the new relay straight down until it clicks into place. Make sure it sits flush.
Step 7 — Reinstall the seat cushion.
Align the clips and press down firmly on the cushion until it locks. Give it a tug to confirm it is secure.
Common Symptoms That Point to the Relay or Fuse Block
Not every no-start or fuel issue traces back to the relay. But if your DTS has any of the following, the rear fuse block should be near the top of your list:
1. Engine cranks but will not start.
The starter is turning the engine over, but there is no fuel pressure. This is the classic symptom of a fuel pump that is not receiving power, often because the relay is not closing or the fuse block trace is dead.
2. The car dies while driving and restarts later.
Intermittent stalling, especially after the car has warmed up, suggests an overheating relay or a melting fuse block connection.
3. Code P0230 appears.
P0230 is the diagnostic trouble code for the fuel pump relay control circuit. It means the ECM has detected an electrical fault in the relay circuit — either an open, a short, or a poor connection.
4. Long cranking before the engine fires.
A weak or failing relay may not close quickly, delaying fuel pressure buildup. This can also indicate a failing fuel pump check valve, so test the relay before condemning the pump.
Should You Replace the Relay or the Whole Fuse Block?
Here is a practical breakdown of what to do based on what you find:
1. If the relay is burnt or chattering — replace the relay first.
A relay is a wear item. If the contacts are pitted or the coil is weak, a fresh relay often solves the problem. The parts cost is roughly $27, with labor around $95 if a mechanic does it, for a total near $122 to $149 depending on your area.
2. If the relay socket shows melted plastic — do not just replace the relay.
The melted socket is a sign that excessive current flowed through that circuit, damaging the block. A new relay will likely burn out again. In this case, the rear fuse block itself needs to be replaced or bypassed.
3. If the fuel pump fuse is blown — find the short first.
A blown fuse is a symptom, not the root cause. Check the pump wiring for chafing or exposed copper, and test the pump's current draw. A pump that is failing internally can draw more amperage and trip the fuse.
4. If everything checks out but the car still will not start — test fuel pressure.
Use a fuel pressure gauge on the rail. The 2009 DTS should read between 384 and 425 kPa (55–62 psi) when the pump runs, and it should hold pressure without dropping more than 34 kPa (5 psi) in one minute. If the pressure is low or drops quickly, the issue is the pump module, the regulator, or a leaking line—not the relay.
Why the Relay Fails on This Platform
The 2009 DTS is a heavy, full-size luxury sedan with a 4.6L V8. It demands a high fuel flow rate at all times, and the fuel pump runs almost continuously while the engine is on. That places constant load on the relay contacts. Over time, the contacts can arc and pit, increasing resistance. Higher resistance means more heat, and more heat accelerates the failure of both the relay and the surrounding fuse block plastic.
There is also a documented issue with the rear underseat fuse block's internal connections melting. GM has not issued a recall for this issue as of the latest owner reports, and even dealerships have stated that no recall exists for the fuse box. That means you are responsible for catching the problem early to avoid a no-start situation in traffic.
KEMSO Fuel Pump: A Reliable Replacement Option
If your diagnosis leads you to replace the fuel pump itself — or if you want a high-performance upgrade while you are already in the fuel system — consider a KEMSO fuel pump. KEMSO builds high-performance fuel pumps designed as OEM replacements, meaning they match factory specifications for fit, flow rate, and pressure while offering improved durability in demanding driving conditions. Every KEMSO fuel pump comes with a lifetime warranty, so you only buy it once. Whether you are restoring a daily driver or plan to push your DTS harder than factory spec, KEMSO gives you a dependable fuel delivery solution that protects your engine from lean conditions caused by a weak or aging pump. You can browse the full lineup of KEMSO fuel pumps at https://www.kemsoracing.com/ — their product catalog covers a wide range of vehicles, and each listing specifies compatibility so you can confirm the correct part for your 2009 Cadillac DTS.
A Quick Safety Note
Working on the fuel system carries real risk. Before you start, relieve fuel pressure by removing the fuel pump fuse and cranking the engine until it dies, then turn the ignition off. Work in a well-ventilated area, keep a fire extinguisher nearby, and disconnect the battery negative terminal before touching any electrical components.
Also, never bypass the fuel pump relay with a jumper wire that is not fused. If you use a fused jumper, make sure it is rated for at least 15A. An unfused jumper can start a fire if the pump circuit shorts out.
Final Thoughts
The fuel pump relay on a 2009 Cadillac DTS sits under the rear seat, inside the driver's side underseat fuse block, specifically as relay #59 with fuse #1 nearby. That location is unusual compared to older GM cars, but it is well-documented once you know where to look. Before you spend money on a fuel pump, check the relay, the fuse, and — most importantly — the condition of the fuse block sockets. In many real-world cases, the relay is merely a victim of a larger issue: a melted internal trace in the rear fuse block that cuts power to the pump entirely. If you catch that early, you can fix the problem with a relay swap or a fused bypass wire. If you let it go too long, you may be looking at a $700+ fuse block replacement.
And if the fuel pump is the confirmed culprit, remember KEMSO offers high-performance, OEM-replacement pumps with a lifetime warranty. Visit https://www.kemsoracing.com/ to find the right pump for your DTS and get back on the road with confidence.