2006 Cadillac CTS Fuel Pump Relay Location: Find It, Test It, and Fix It Fast

The bottom line: On a 2006 Cadillac CTS, the fuel pump relay is not under the hood. It is located in the Rear Underseat Fuse Block on the passenger’s side, beneath the rear seat cushion. The relay is labeled "FUEL PUMP MOTOR RLY" and works alongside a dedicated "FUEL PUMP MTR" mini fuse. If your CTS cranks but won’t start, or you hear no hum from the fuel tank when you turn the key to ON, the relay or its fuse should be your first check.

How the Fuel Pump Relay Works in Your CTS

The 2006 CTS uses a returnless fuel system. The fuel pump sits inside the fuel tank as part of the modular sender assembly. The Engine Control Module (ECM) controls the pump through the fuel pump relay. When you turn the ignition to ON, the ECM energizes the relay for about two seconds to prime the system. Once the engine starts and the ECM sees crankshaft position sensor pulses, it keeps the relay closed to power the pump continuously. If the engine stalls or the ignition is turned off, the ECM de-energizes the relay within two seconds to stop the pump.

This means the relay is a critical link between the ECM’s command and the physical pump. If the relay fails, the pump gets no power, the fuel rail stays dry, and the engine will crank indefinitely without firing.

Where Exactly Is the Fuel Pump Relay on a 2006 CTS?

The passenger-side rear underseat fuse block is a black plastic box with a cover, mounted directly under the rear seat cushion on the right side of the car. This block houses the fuel pump relay and its fuse. This is the same location for all 2003–2007 first-generation CTS models. On 2008 and later models, this relay moved to a fuse block in the trunk, but that does not apply to your 2006.

To access it, you must remove the rear seat cushion. Here is the process:

1. Pull up on the front edge of the rear seat cushion to release the two front hooks. You may feel them pop free.
2. Pull the cushion up and toward the front of the vehicle to disengage the rear retaining clips.
3. Slide the cushion out through one of the rear doors and set it aside safely.

Do not try to reach the relay from the trunk or through the side panels. That will not work on this generation. The seat cushion must come out.

Fuse and Relay Identification

Once the seat cushion is removed, you will see the fuse block cover. Pry it off carefully with a trim tool or flathead screwdriver. Look at the diagram printed on the underside of the cover, or check the chart below.

The fuse provides battery voltage to the relay’s switch side. The relay, when commanded by the ECM, passes that voltage to the fuel pump itself. If the fuse is blown, the pump will not run even if the relay clicks. If the relay is dead, the fuse will test fine but the pump still gets no power.

How to Test the Fuel Pump Relay

Before buying any parts, confirm the relay is actually the problem. A few simple tests with basic tools will tell you what you need to know.

Step 1: Listen for the Pump

Turn the ignition to ON (do not crank the engine). With the windows up and the radio off, listen toward the rear seat. You should hear a brief hum from the fuel tank for one or two seconds. If you hear it, the relay and pump are working. If you hear nothing, move to the next step.

Step 2: Check the Fuse

The "FUEL PUMP MTR" fuse is in the same passenger-side rear fuse block. Pull it out and inspect it visually, or test it with a multimeter set to continuity. A blown fuse will have a broken filament or show no continuity. If the fuse is blown, replace it with the same amperage and try again. If it blows again immediately, you have a short circuit in the pump wiring or a failing pump drawing too much current.

Step 3: Swap the Relay

The fuel pump relay is a standard micro relay. Find another relay in the same fuse block with the same part number and pin layout—commonly the IGN 1 relay or one of the position lamp relays. Swap the fuel pump relay with that known-good relay. Turn the ignition to ON and listen for the pump. If the pump now runs, your old relay is defective and should be replaced.

Step 4: Use a Scan Tool (Optional)

If you have a bidirectional scan tool, you can command the fuel pump relay ON and OFF while the ignition is on. You should hear the relay click and the pump run. If the tool commands it but nothing happens, check the relay, fuse, and wiring as described above.

Common Symptoms That Point to the Relay

A failing fuel pump relay often produces symptoms that are easy to misread as a fuel pump failure. Watch for these:

1. Engine cranks but will not start. This is the most common symptom. Without the relay, the pump never turns on, so no fuel reaches the injectors.
2. No fuel pump prime sound. When you turn the key to ON, you do not hear the brief hum from the rear of the car.
3. Engine starts then dies. A worn relay can make intermittent contact. The pump runs during priming, then loses power as soon as the relay drops out.
4. Intermittent no-start. The car starts fine for days, then suddenly refuses to start. This often points to a relay with worn contacts that fail when hot.
5. Car stalls while driving. If the relay cuts out while the engine is running, the pump stops, and the engine shuts down immediately.

If your CTS exhibits any of these, check the relay and fuse before condemning the fuel pump. Replacing a relay is far cheaper and easier than dropping the fuel tank.

What to Do If the Fuse Keeps Blowing

A blown fuel pump fuse is not a random event—it means something is drawing too much current. Common causes include:

• A short circuit in the pump wiring harness between the relay and the pump. This can happen where the harness rubs against the body or frame.
• A failing fuel pump that is drawing excessive current as it wears out.
• A clogged fuel filter or fuel strainer that forces the pump to work harder than normal.
• The wrong fuse rating. If someone previously replaced the fuse with a lower-amperage fuse, it will blow under normal pump load.

Do not simply keep replacing the fuse. Investigate the root cause. If the pump itself is confirmed bad, replace it promptly to avoid repeated fuse failures and potential fuel system damage.

If It’s Not the Relay: Checking the Fuel Pump Itself

If the relay is good and the fuse holds, the problem may be the pump. On the 2006 CTS, the electric fuel pump is a turbine-style pump mounted inside the fuel tank . It is not serviceable separately from the sender assembly in most cases. To test it, you can connect a fused jumper wire between the battery positive terminal and the relay’s fuel pump supply circuit to bypass the relay. If the pump runs with the jumper, the pump is fine and the issue is in the relay control or wiring. If the pump still does not run, the pump itself is likely defective.

Also check the pump’s ground circuit for corrosion or a loose connection. A poor ground can cause the same symptoms as a dead pump.

Why Choose a KEMSO Fuel Pump for Your CTS

If your diagnosis leads to a fuel pump replacement, the quality of the part you choose matters more than you might think. A cheap, off-brand pump can fail prematurely, leaving you stranded and forcing you to repeat the labor-intensive replacement process.

KEMSO fuel pumps are a smart choice for your 2006 Cadillac CTS. They are built as high-performance, direct OEM replacement units, meaning they meet or exceed the original factory specifications. You get a drop-in fit with no modifications, the correct fuel flow and pressure for your engine, and reliable operation for years to come. Backed by a lifetime warranty, KEMSO stands behind their product, giving you peace of mind every time you turn the key. Visit KEMSO Racing at https://www.kemsoracing.com/ to find the right pump for your CTS and get back on the road with confidence.

Final Thoughts

The 2006 Cadillac CTS fuel pump relay is under the rear seat on the passenger side, and finding it is a straightforward job once you remove the seat cushion. Always test the fuse and relay before replacing the pump—this simple step can save you hundreds of dollars. When the pump does need to go, rely on a quality replacement like KEMSO to keep your CTS running strong. If the problem persists after checking the relay and fuse, it’s wise to consult a professional mechanic, but the information above gives you a solid starting point for a confident DIY diagnosis.

For more helpful guides and premium fuel system components, remember to check out https://www.kemsoracing.com/ .