Replacing The Fuel Pump In Your Mercedes 126: A Step-By-Step Guide

Replacing the fuel pump on a Mercedes 126 can be a complex process. Before starting, it is important to disconnect the battery and ensure the area is well-ventilated to prevent any risk of fire or explosion. The next steps involve accessing the fuel pump by removing the rear passenger seat and protective liner, and then using tools such as pliers, ratchets, and screwdrivers to undo the bolts and remove the fuel pump. When removing the fuel pump, be cautious as it may drip fuel. The new pump can then be installed in the reverse order, ensuring all components are securely connected and no leaks are present. It is also recommended to replace the fuel filter and hoses at the same time if they have not been replaced recently.

Characteristics of replacing the fuel pump on a Mercedes 126:

Disconnect the negative battery terminal and insulate

Disconnecting the negative battery terminal and insulating it is a crucial step when working on your car, especially when dealing with fuel pumps or other electrical components. Here are some detailed instructions on how to safely perform this task on a Mercedes 126:

Park Your Vehicle and Engage Parking Brakes:

Before starting any work on your Mercedes 126, it's essential to ensure the car is securely parked with the parking brakes engaged. This step helps prevent any accidental movement of the vehicle during the repair process.

Locate the Battery:

The battery's location can vary depending on the model of your Mercedes 126. In most cases, it is found in the trunk on the right side. However, some models, such as the W203 and R170, have the battery in the engine bay or passenger side. Consult your owner's manual if you're unsure of the exact location.

Disconnect the Negative Battery Terminal:

With the car securely parked, locate the negative battery terminal. It is usually marked with a "-" symbol and may have a black plastic cap. Using an appropriate-sized wrench, loosen the 10mm bolt on the negative terminal first. Then, carefully pull the terminal away from the post. If it doesn't come out easily, try twisting it gently and then pulling again. Ensure that you don't use excessive force, as it can damage the terminal. If the battery cable clamp is stuck, consider using a battery terminal puller to detach it safely.

Insulate the Negative Terminal:

Once the negative terminal is disconnected, it's crucial to insulate it properly. Cover the terminal with electrical tape or any suitable insulating material. This step ensures that the negative terminal doesn't accidentally come into contact with the car's frame or any metal parts, which could lead to a short circuit or electrical issues.

Secure the Insulation:

After insulating the negative terminal, make sure it is securely taped or covered. Ensure that the insulation doesn't slip off or move during the rest of the repair process. This precaution will help prevent any accidental electrical connections that could be hazardous.

Proceed with Caution:

Working on a car's electrical system, especially the battery, demands caution. Always follow established safety protocols and refer to your car's repair manual for specific instructions pertaining to your Mercedes 126 model. Ensure that you wear appropriate safety gear, such as gloves and safety goggles, when handling the battery and its terminals.

Remove rear seats and rear seat bottom covers

To remove the rear seats and rear seat bottom covers of your Mercedes 126, follow these steps:

Step 1: Remove the flaps of the rear seats.

Locate the access site for the fuel pump, which is under the rear seats. Remove the flaps of the rear seats to access this area.

Step 2: Remove the rear seat bottom covers.

The rear seat bottom covers are held in place by tabs, not screws. Releasing these tabs is the most challenging part of the process, as they can easily break. Work slowly and carefully to avoid breaking the tabs. There are detailed instructions available in a PDF guide, which you can refer to for this step.

Step 3: Unscrew and disconnect the rear seats.

There are two hex nuts and several torx bolts holding the rear seats in place. Unscrew these and disconnect the SRS cables (one for each seat) to remove the seats.

Step 4: Remove the 40% seat (rear passenger side) from the car.

The 60% seat is very heavy, so it's recommended to slide it towards the 40% seat to make it easier to work on the driver's side.

Now you will be able to access the fuel pump and continue with the replacement procedure.

Disconnect the electrical wiring at the fuel pump(s)

Disconnecting the electrical wiring at the fuel pump(s) is a crucial step in replacing the fuel pump on a Mercedes 126. Here is a detailed, step-by-step guide to help you through the process:

Before beginning any work on your Mercedes 126, it is important to take the necessary safety precautions. Make sure the car is parked on a flat surface and the parking brake is engaged. Wear protective gear, such as gloves and eye protection, and place a suitable container to catch any fuel spillage.

Now, let's get started:

• Remove the fuel tank filler cap: This step is important to depressurize the fuel tank before proceeding.
• Disconnect the negative battery terminal: Ensure that you insulate the terminal after disconnection.
• Remove the fuel pump assembly cover: This will give you access to the fuel pump and its components.
• Pinch off the fuel suction and delivery hoses: Use an appropriate clamping tool for this step. Be cautious, as high-pressure fuel may be released when disconnecting the fuel delivery lines.
• Remove the metal fuel line: Disconnect the metal fuel line that connects the fuel accumulator, fuel filter, and fuel pump.
• Disconnect the electrical wiring: This is the critical step we are focusing on. Carefully disconnect the electrical wiring at the fuel pump(s). You may need to unplug a cable that serves as the power line to the pump.
• Remove the fuel pump connecting line: If there are two fuel pumps, loosen and remove the connecting line between them.
• Note the position of the fuel pump(s): Pay attention to the position of the fuel pump(s) and any insulating sleeve(s) before removal.

By following these steps, you will have successfully disconnected the electrical wiring at the fuel pump(s) of your Mercedes 126. Remember to work carefully and refer to a qualified mechanic or a detailed guide if you need further assistance.

Remove the fuel pump connecting line

To remove the fuel pump connecting line, follow these steps:

First, ensure you have the right tools. You will need an appropriate clamping tool to pinch off the fuel suction and delivery hoses. You can use a pair of vise grips.

Next, locate the fuel pump connecting line. It is between fuel pumps M3/1 and M3/2.

Now, remove the line. When disconnecting the fuel delivery lines, be aware that high-pressure fuel may be released. Always use new sealing rings when reconnecting metal fuel lines.

Finally, check for leaks. Once you have finished, run the engine and check for any fuel leaks.

Remove and replace the fuel pump

To remove and replace the fuel pump in a Mercedes 126, follow these steps:

Firstly, ensure you are working in a well-ventilated area and have access to a fire extinguisher. There should be no sources of static electricity, smoke, or fire.

Now, onto the car. Start by removing the fuel tank filler cap to depressurise the fuel tank. Next, disconnect the negative battery terminal and insulate it. Then, remove the fuel pump assembly cover. With an appropriate clamping tool, pinch off the fuel suction and delivery hoses.

When disconnecting the fuel delivery lines, be aware that high-pressure fuel may be released. Remove the metal fuel line that connects the fuel accumulator, fuel filter, and fuel pump. Then, remove the fuel suction hose from the fuel pump. Disconnect the electrical wiring at the fuel pump(s).

At this stage, you can remove the fuel pump(s) by loosening the mounting screws on the fuel pump bracket. Note the position of the fuel pump(s) and insulating sleeve(s) before removal.

To install the new fuel pump(s), follow these steps in reverse. Always use new sealing rings when reconnecting metal fuel lines. Ensure you run the engine and check for fuel leaks.

Alternatively, if you are removing and replacing the fuel pump in a Mercedes E-Class (2002-2009), follow these steps:

Disconnect the battery before commencing any work. Start by disconnecting the negative (black) terminal, then the positive (red) terminal.

Access the rear passenger seat and lift up the bottom part of the seat—the seats will swing toward the driver's seat backrest. Then, remove the protective liner and use pliers to pop the metal lid above the fuel pump. Use a ratchet and socket to undo the six bolts that keep the fuel pump sealed.

Now that you can access the fuel pump, you need to disconnect the following components:

• Fuel line (black rubber hose)
• Wiring harness (white plastic plug with red and black wires)
• Holding brackets (one on each side of the pump)

Use pliers to push on the side clips of the wiring harness to remove it, then use a flathead screwdriver to push on the green pin on the fuel line connector to slide it off. Then, use your fingers to twist the holding brackets until they unsnap. Now, you can slide the fuel pump out. Be careful, as it may drip some fuel.

To install the new fuel pump, follow these steps in reverse.

Frequently asked questions