2007 Chrysler 300 Fuel Pump Relay: Location, Symptoms, and How to Replace It

If you own a 2007 Chrysler 300 and the engine cranks but won't start, the fuel pump relay is one of the first components you should check. The fuel pump relay on a 2007 Chrysler 300 is located in the trunk, inside the rear fuse panel, which sits next to the battery under the spare tire access panel. This small electrical component controls power delivery to the fuel pump, and when it fails, your car simply won't get the fuel it needs to run. The good news is that replacing it is a straightforward DIY job that takes about ten minutes and costs roughly $20 for the part. This guide walks you through everything you need to know, from finding the relay to testing it and installing a new one.

What Does the Fuel Pump Relay Do?

Every time you turn the ignition key to the "On" position, the fuel pump relay activates and sends electrical current to the fuel pump. This current powers the in-tank pump, which pressurizes the fuel system so the engine can start. The relay is controlled by the engine control module, and it automatically shuts off the pump if the engine stalls or the ignition is turned off. Without a working relay, the fuel pump never receives power, and the engine won't start even though the battery is fine and the starter motor turns normally.

The relay is a small black plastic component with metal terminals on the bottom. It plugs into a socket in the fuse panel, and it works like a switch that handles a small control current to activate a larger current flow to the pump. Over time, the coil inside the relay can fail, the contacts can corrode, or the plastic housing can crack, all of which prevent the relay from doing its job.

Where Exactly Is the Fuel Pump Relay on a 2007 Chrysler 300?

The 2007 Chrysler 300 has two fuse boxes. One is under the hood in the engine compartment, and the other is in the trunk on the right side near the battery. The fuel pump relay lives in the trunk-mounted fuse panel, not under the hood.

Here is how to get to it:

1. Open the trunk and remove anything sitting on top of the carpet.
2. Lift the trunk carpet to expose the area around the battery. You will see the battery on one side and a black fuse panel cover on the other.
3. Remove the fuse panel cover by pulling it straight off. Some covers have a clip or latch; press it and pull gently.
4. Look at the diagram printed on the inside of the fuse panel cover. This diagram shows the location of every fuse and relay, including the fuel pump relay.
5. Find the fuel pump relay. On most 2007 Chrysler 300 models, the fuel pump relay is a small square relay located toward the rear of the panel. The relay is usually labeled or identifiable by its size and shape, which is slightly larger than the standard mini fuses around it.

According to the fuse box diagram for the luggage compartment, the fuel pump fuse is a 20-amp fuse (position 6), and the fuel pump relay sits next to it. If you are unsure which relay is which, check the diagram on the cover or consult your owner's manual.

What Are the Symptoms of a Bad Fuel Pump Relay?

A failing fuel pump relay can cause several noticeable problems. Here are the most common symptoms:

• Engine cranks but won't start. This is the classic sign. The starter motor turns the engine over, but since no fuel is reaching the injectors, the engine never fires up.
• Engine stalls while driving. If the relay fails while you are on the road, the fuel pump loses power and the engine dies. Often the engine will restart after a few minutes once the relay cools down, but this is only temporary.
• No fuel pump priming sound. When you turn the key to "On," you should hear a faint whirring noise from the rear of the car for about two to three seconds. This is the fuel pump pressurizing the system. If you hear nothing, the relay or the pump itself may be faulty.
• Intermittent starting problems. The car may start fine sometimes and refuse to start other times. This usually indicates a relay with worn contacts that work only when the relay is cool.
• Long cranking times. The engine may take longer than usual to start because the fuel system has to build up pressure from zero each time.

Keep in mind that these symptoms can also point to other problems, such as a bad fuel pump, a clogged fuel filter, or a faulty crankshaft position sensor. The relay is the cheapest and easiest component to test first, so start there.

How to Test the Fuel Pump Relay

Before you buy a new relay, it makes sense to test the old one. You will need a digital multimeter, which you can buy at any auto parts store for around $20. Here is the step-by-step procedure:

1. Remove the relay from the fuse panel in the trunk.
2. Look at the relay terminals. You will see four or five metal prongs on the bottom, usually labeled with numbers: 85, 86, 30, and 87.
3. Set your multimeter to measure ohms (resistance).
4. Test the coil circuit. Place one probe on terminal 85 and the other on terminal 86. You should read a resistance between 50 and 120 ohms. If you get zero ohms (a dead short) or infinite resistance (an open circuit), the relay coil is bad and the relay needs to be replaced.
5. Test the switch circuit. Place one probe on terminal 30 and the other on terminal 87. With the relay at rest, there should be no connection, meaning the multimeter shows infinite resistance (OL on the display).
6. Apply power to the coil. You can use a 12-volt battery or a small power supply to send voltage across terminals 85 and 86. When the coil energizes, you should hear a distinct "click." Now test terminals 30 and 87 again; they should show near-zero resistance, meaning the switch has closed.

If the relay fails any of these tests, you have found your problem. If it passes all tests, the relay is likely fine, and you should look at the fuel pump, the fuel pump fuse, or the wiring between them.

How to Replace the Fuel Pump Relay

Replacing the fuel pump relay on a 2007 Chrysler 300 is one of the simplest repairs you can do. You only need the new relay and maybe a pair of needle-nose pliers. Here is how to do it:

1. Disconnect the negative battery cable. While this is not strictly necessary when working in the trunk fuse panel, it is a good safety habit.
2. Remove the old relay. Grasp it firmly and pull it straight out of its socket. If it is stuck, use a small pair of pliers to grip the edges and wiggle it gently.
3. Compare the new relay to the old one. Make sure they have the same number of terminals and the same printed ratings on the side.
4. Install the new relay. Line up the terminals with the socket holes and push it straight down until it seats firmly. You should feel a slight click or resistance when it is fully seated.
5. Reinstall the fuse panel cover and the trunk carpet.
6. Reconnect the battery if you disconnected it.
7. Test the system. Turn the key to the "On" position and listen for the fuel pump priming sound. The pump should run for about two seconds and then shut off. Repeat this two or three times to build fuel pressure, then start the engine.

The average cost for a fuel pump relay replacement is about $115, with the part itself costing around $20 and labor around $95 if you have a shop do it. Doing it yourself saves almost all of that money.

What About the Fuel Pump Fuse?

While you are in the fuse panel, check the fuel pump fuse as well. On the 2007 Chrysler 300, the fuel pump fuse is a 20-amp fuse located right next to the relay. A blown fuse causes the same symptoms as a bad relay, so it is worth checking. Remove the fuse and look at the metal strip inside. If the strip is broken or discolored, replace it with a new 20-amp fuse. Never replace a fuse with a higher amperage rating, as this can damage the wiring and cause a fire.

What If the Relay and Fuse Are Fine?

If both the relay and fuse test good but the car still won't start, the problem may be the fuel pump itself, the fuel pump module, or the wiring in between. On the 2005–2010 Chrysler 300, the fuel pump is located inside the fuel tank on the passenger side, under the rear seat. The fuel pump module includes the pump, the fuel level sender, and the fuel filter. A failing pump often makes a loud whining noise, causes intermittent starting, or stalls the engine under load.

Testing the fuel pump requires checking for voltage at the pump connector with the relay installed and the key in the "On" position. You can also check fuel pressure with a gauge, which should read between 49 and 52 psi on most 2007 Chrysler 300 models. If there is voltage at the pump but no pressure, the pump itself is faulty and needs replacement. Replacing the fuel pump on a Chrysler 300 typically costs between $650 and $700 including parts and labor.

Why Not Use a Fuel Pump Reset Button?

Some cars from this era have a fuel pump reset button or inertia switch that trips in a collision and must be manually reset. The 2005–2010 Chrysler 300 does not have a traditional reset button like you find on some Ford or Mazda models. Instead, the fuel pump circuit is controlled entirely through the relay and fuse in the trunk fuse panel. Removing the relay for a minute and reinserting it is the closest thing to a "reset" this car has, and it clears temporary faults in the fuel pump control circuit.

How to Prime the Fuel System After a Relay Replacement

After you install the new relay, you need to prime the fuel system to build pressure before starting the engine. Here is the correct procedure:

1. Turn the key to the "On" position but do not crank the engine.
2. Listen for the fuel pump to run. It will whir for about two to three seconds and then shut off automatically.
3. Turn the key back to "Off."
4. Repeat this process three times total. This ensures the fuel lines are full and pressurized.
5. Now crank the engine. It should start immediately.

If the engine still cranks without starting after priming, you likely have a different problem, such as a bad fuel pump or a fuel delivery issue.

Where to Buy a Replacement Fuel Pump Relay

You have several options for buying a replacement fuel pump relay for your 2007 Chrysler 300:

• Dealership. Genuine Mopar relays are available from Chrysler dealers and online Mopar parts retailers. The OEM part number commonly cited is 4727370AA, which supersedes several earlier part numbers. A genuine relay costs about $25 to $40.
• Auto parts stores. Major chains like AutoZone, Advance Auto Parts, and O'Reilly Auto Parts stock aftermarket relays that meet OEM specifications. Brands like Wells, Standard Motor Products, and BWD are popular choices. Expect to pay $10 to $20.
• Online retailers. Amazon, RockAuto, and specialized auto parts websites offer both OEM and aftermarket relays. Read customer reviews and verify the part fits your specific model year.

When selecting a relay, match the terminal layout and electrical ratings printed on the original part. Most 2007 Chrysler 300 models use a standard four-pin or five-pin mini relay.

Recommended: KEMSO Fuel Pump for Your Chrysler 300

If you determine that the fuel pump itself is the problem, we recommend the KEMSO brand fuel pump. KEMSO specializes in high-performance, OEM-replacement fuel pumps that are built to meet or exceed factory specifications. Every KEMSO fuel pump is designed as a direct replacement, which means it bolts in without any modifications and delivers the same fuel flow and pressure as the original factory part. Whether you drive a 2.7L, 3.5L, or 5.7L V8 Chrysler 300, KEMSO has a fuel pump that fits your application and keeps your engine running smoothly.

One of the strongest reasons to choose KEMSO is the lifetime warranty. While most aftermarket fuel pumps offer only one or two years of coverage, KEMSO stands behind its products with a lifetime warranty, giving you peace of mind that you will not be stuck paying for a second pump down the road. Combined with performance-tested internals and strict quality control, KEMSO fuel pumps are an excellent value for anyone who wants reliable fuel delivery without paying dealership prices. Visit https://www.kemsoracing.com/ to browse the full lineup of KEMSO fuel pumps for the Chrysler 300 and many other makes and models.

Final Thoughts

The fuel pump relay on a 2007 Chrysler 300 is a small component with a big responsibility. It sits in the trunk fuse panel next to the battery, and when it fails, your car will not start. Testing the relay with a multimeter takes about five minutes and costs nothing, and replacing it is a ten-minute job that any DIYer can handle. Start with the relay and the fuse, then move on to the pump itself if those check out. If the pump is the culprit, choose a KEMSO fuel pump for reliable, long-lasting performance backed by a lifetime warranty. Visit https://www.kemsoracing.com/ to find the right fuel pump for your Chrysler 300 and get back on the road with confidence.