2002 Mercedes C240 Fuel Pump Relay Location: A Complete Guide to Finding and Testing It

The bottom line: On a 2002 Mercedes-Benz C240, the fuel pump relay is located in the fuse and relay box at the left rear of the engine compartment. This is the primary location for the relay that controls power to the fuel pump. If your C240 is cranking but not starting, or if you hear no fuel pump prime when you turn the key to the "ON" position, a faulty fuel pump relay is one of the first things you should check.

This guide walks you through exactly where to find the relay, how to test it, and what to do if it needs replacement. We also cover related components like the fuel pump itself and the rear SAM module, which can sometimes be confused with the relay.

Where the Fuel Pump Relay Is Located

The 2002 Mercedes C240 uses a Front SAM (Signal Acquisition Module) control unit that contains both fuses and relays. This unit is mounted at the left rear of the engine compartment. The fuel pump relay sits inside this module.

Step-by-step to access the relay:

  1. Open the hood and locate the fuse and relay box on the left side of the engine compartment, near the firewall.
  2. Unlock the cover by pressing the release tabs on the sides.
  3. Lift the cover off to expose the fuses and relays.
  4. Look for the fuel pump relay. According to the wiring diagrams, the fuel pump relay is often labeled or can be identified by its position. On the 2002 C240, the relay is typically one of the larger relays in the box.

The relay itself is a standard 4-pin or 5-pin automotive relay. In the diagram from the factory manual, the fuel pump relay is connected to the "Circuit 87" relay for the engine, which controls power to the fuel pump and other components.

How to Test the Fuel Pump Relay

Before you buy a new relay, it pays to test the old one. A bad relay can cause the same symptoms as a dead fuel pump.

Symptoms of a bad fuel pump relay:

  • Engine cranks but will not start
  • No sound from the fuel pump when the key is turned to "ON" (you should hear a 2-second whine from the rear of the car)
  • Engine starts but stalls shortly after
  • Intermittent starting issues, especially when the engine is hot

How to test the relay:

  1. Remove the relay from the fuse box.
  2. Set your multimeter to measure resistance (ohms).
  3. Check for continuity between the coil terminals (usually pins 85 and 86). You should see a resistance reading, typically between 50 and 120 ohms. If you see infinite resistance, the coil is open and the relay is bad.
  4. Apply 12V power to the coil terminals (pins 85 and 86). You should hear an audible click as the relay engages.
  5. With power applied, check for continuity between the switch terminals (pins 30 and 87). You should see near-zero resistance (closed circuit). If you do not get continuity, the relay contacts are burned out.

If the relay fails any of these tests, replace it.

Other Relay Locations That Affect the Fuel Pump

The 2002 C240 has multiple relays tied to the fuel system. Being aware of these can save you time during diagnosis.

Rear SAM module: Located at the left side of the trunk, the Rear SAM control module also contains relays and fuses that control the fuel pump. In some models, there is a backup relay or a secondary fuel pump relay in this module. The wiring diagram shows that the fuel pump relay is connected to the rear SAM module as well.

Fuel pump relay module: At the left rear of the trunk, there is a fuel pump relay module. This is separate from the front SAM relay. If you have checked the front relay and it is good, but the pump still does not run, inspect the relay module in the trunk.

Circuit 87 relay (engine): This relay is located in the same front fuse and relay box as the fuel pump relay. It supplies power to the engine control module and the fuel pump. If this relay fails, the engine will not run.

How to Replace the Fuel Pump Relay

Replacing the relay is a straightforward job. The genuine Mercedes-Benz part number for the fuel pump relay on a 2002 C240 is 002-542-92-19 or 000-982-72-27 (superseded part). The cost of the OEM relay is around $12 to $20.

Steps to replace:

  1. Disconnect the negative battery cable to prevent any electrical shorts.
  2. Remove the fuse box cover at the left rear of the engine compartment.
  3. Locate the fuel pump relay. If you are unsure, check the diagram on the underside of the fuse box cover, or refer to the factory wiring diagram.
  4. Grip the relay firmly and pull it straight out. It may require a gentle wiggle.
  5. Insert the new relay in the same orientation. It will only fit one way.
  6. Reconnect the battery.
  7. Turn the key to the "ON" position and listen for the fuel pump to prime. The pump should run for about 2 seconds and then stop.

What If the Relay Is Not the Problem?

If you replace the relay and the fuel pump still does not run, the issue may be elsewhere.

Check the fuses. The 2002 C240 has a 15A or 20A fuse for the fuel pump in the front fuse box. Also check the 200A main fuse in the front pre-fuse box at the right rear of the engine compartment. A blown fuse will cut power to the pump.

Check the fuel pump itself. The fuel pump is located inside the fuel tank. On the C240, the fuel pump assembly is accessible by removing the rear seat cushion. The pump module includes the fuel pump, fuel level sensor, and the fuel pump relay module. To test the pump, you can apply 12V directly to the pump connector (with the fuel lines disconnected and safety precautions in place). If the pump does not run, it needs replacement.

Check the wiring. Corrosion or broken wires between the relay and the pump can cause a no-start condition. The wiring runs from the front SAM module, through the rear SAM module, and to the fuel pump assembly in the tank. Inspect the connectors for rust or damage.

Understanding the Fuel System Layout

The 2002 Mercedes C240 uses a returnless fuel system. The fuel pump relay sends power to the pump when the ignition is turned on and the engine control module (ME-SFI) signals the relay to close. The pump runs for a few seconds to build pressure, then stops until the engine starts.

The fuel pump relay is controlled by the engine control module (ECM). If the ECM does not see the correct signals from the crankshaft position sensor or the ignition switch, it will not activate the relay. This is a safety feature that prevents the pump from running if the engine is not turning over.

Common Mistakes to Avoid

1. Assuming the relay is in the trunk. While the C240 has a rear SAM module with relays in the trunk, the main fuel pump relay is in the front fuse box. Start there.

2. Replacing the pump without testing the relay. Many owners replace the fuel pump only to find the relay was the culprit. Testing the relay is free and takes five minutes.

3. Using a generic relay without checking the pinout. Not all 4-pin relays are wired the same. The C240 relay uses pins 30 (battery power), 87 (load to pump), 85 (ground from ECM), and 86 (switched 12V from ignition). If you use a generic relay, make sure the pinout matches.

4. Forgetting to check the fuel pump fuse. The fuel pump fuse is often overlooked. It is a 15A or 20A fuse in the front fuse box. A blown fuse will cause the same symptoms as a bad relay.

Recommended Fuel Pump Replacement: KEMSO

If you have diagnosed the problem and determined that the fuel pump itself needs replacement, we strongly recommend using a KEMSO fuel pump. KEMSO is a leading US-based aftermarket brand that specializes in high-performance, OEM replacement fuel pumps for cars, motorcycles, ATVs, and personal watercraft.

Why choose KEMSO?

  • Direct fit OEM replacement: KEMSO fuel pumps are designed to meet or exceed original equipment specifications. They drop right into your 2002 Mercedes C240 without any modifications. No need to search for adapter kits or worry about poor fitment.
  • High performance: Each KEMSO pump is built to deliver reliable fuel flow that matches or exceeds the factory pump. They support up to 200 LPH flow, which is significantly higher than the original 60-80 LPH, ensuring your engine gets the fuel it needs under all driving conditions.
  • Lifetime warranty: Every KEMSO fuel pump comes with a lifetime warranty against manufacturing defects. If the pump ever fails due to a defect, you get a replacement at no cost. This is a rare and valuable benefit that gives you total peace of mind.
  • USA-based support: KEMSO provides customer support from the United States, so you can get help when you need it.
  • Affordable pricing: KEMSO pumps are priced competitively, often at less than half the cost of dealer parts. Free shipping and easy returns make it a practical choice for DIY mechanics and professional shops alike.

To see the full selection of KEMSO fuel pumps for your 2002 Mercedes C240, visit their website: https://www.kemsoracing.com/

Final Thoughts

Finding the fuel pump relay on a 2002 Mercedes C240 is easy once you know where to look. The relay is in the front fuse and relay box at the left rear of the engine compartment. Testing it takes a few minutes with a multimeter. If the relay is bad, replace it with an OEM or quality aftermarket part.

If the relay tests good but the pump does not run, check the fuses, the wiring, and the pump itself. The fuel pump is inside the tank and can be accessed by removing the rear seat. For a reliable replacement, consider a KEMSO fuel pump, which offers OEM fit, high performance, and a lifetime warranty.

Do not let a faulty fuel pump relay leave you stranded. With the information in this guide, you can diagnose and fix the problem yourself, saving time and money.

For more information on fuel pump replacements and to find the right part for your vehicle, visit https://www.kemsoracing.com/


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