Replacing The Fuel Pump In Your Mercedes Ml320: Step-By-Step Guide

If you're experiencing issues with your Mercedes ML320's fuel pump, you may need to replace it. The fuel pump is responsible for delivering fuel from the tank to the fuel injectors. A failing fuel pump can cause a loss of engine power, prevent the car from starting, or cause the check engine light to come on.

You can replace the fuel pump yourself, but caution is advised due to the risk of fire. The process involves disconnecting the battery, removing an access cover (usually located under the rear seat), and replacing the pump and pre-pump filter screen. When replacing the pump, it is recommended to also replace the fuel filters and the fuel pump relay.

The cost of a fuel pump replacement for a Mercedes ML320 ranges from $903 to $954, while parts typically cost around $710. There are several retailers that sell fuel pumps for the ML320, including Amazon, AutoZone, and RepairPal.

Removing rear seats

To remove the rear seats of your Mercedes ML320, you will need to first remove the flaps of the rear seats. This will expose the access site for the next steps.

Next, you will need to remove the rear seat bottom covers. There are no screws holding these in place, just tabs. Be careful when releasing the tabs as they can easily break.

Once the covers are removed, you will see two hex nuts and several torx bolts holding the rear seats in place. You will need to unscrew these and disconnect the SRS cables for each seat.

At this point, you can remove the 40% seat (rear passenger side) from the car. The 60% seat is very heavy, so you will need to slide it to the location of the 40% seat to access the driver's side.

Now you can begin to access the fuel pump. Fold the floor mat in the driver's side corner, and you will see a round cap covering the access hole. This cap is attached to the body by sealant, so be careful when removing it.

With the cap removed, you will see the top of the fuel pump. Before proceeding, it is recommended to take a picture to document the alignment of the pump connections.

Disconnecting cables

Disconnecting the cables is a crucial step in replacing the fuel pump of a Mercedes ML320. Here is a detailed, step-by-step guide on how to do it:

Step 1: Remove the rear seat flaps and the rear seat bottom covers. This can be done by releasing the tabs. Be cautious, as this step is challenging, and the tabs can easily break.

Step 2: Unscrew the rear seats. There are two hex nuts and several torx bolts that need to be removed.

Step 3: Disconnect the SRS cables. There will be one cable for each seat.

Step 4: Remove the seats from the car. The 40% seat (rear passenger side) can be completely removed, while the 60% seat (driver side) is very heavy and should be slid to the location of the 40% seat to provide access to the driver side.

Step 5: Fold the floor mat on the driver's side corner to locate a round cap covering the access hole to the fuel pump. This cap is attached to the body by a sealant.

Step 6: Remove the seal and lift the cap. Underneath, you will see the fuel pump. Take a picture to document the alignment of the pump connections.

Step 7: Unplug the cable, which is the power line to the pump.

Step 8: Start the engine and wait for 5-10 seconds until the engine runs out of fuel and stalls.

Step 9: Disconnect the fuel lines. Push the line and press the tabs on each side with your fingers to remove it. Caution: The feeding line (fuel line in the center) is still pressurized and contains fuel. Place towels around the area and collect the fuel spillage in a cup to minimize inhalation of fuel vapors.

By following these steps, you will successfully disconnect the cables and be ready to remove and replace the fuel pump of your Mercedes ML320. Remember to exercise caution and refer to a professional mechanic if you are unsure about any steps.

Removing seal and cap

To remove the seal and cap of your Mercedes ML320's fuel pump, you will first need to remove the rear seats and seat bottom covers. There are no screws, just tabs, and releasing these is the most challenging step as they break easily. Once you have removed the seats, fold the floor mat in the driver-side corner to reveal a round cap. This cap is attached to the body by a sealant. You can then remove the seal and lift the cap to reveal the fuel pump.

Disconnecting power line and fuel lines

Disconnecting the power line and fuel lines is a crucial step in replacing the fuel pump of a Mercedes ML320. Here is a detailed, step-by-step guide on how to safely and effectively complete this task:

Step 1: Remove the rear seats.

This involves releasing the tabs securing the rear seat bottom covers and then unscrewing the rear seats. Be cautious, as releasing the tabs can be challenging, and it is easy to break them.

Step 2: Move the seats.

The 60% seat (driver's side) is very heavy, so just slide it towards the location of the 40% seat (rear passenger side) to access the driver's side.

Step 3: Access the fuel pump.

Fold the floor mat on the driver's side corner to reveal a round cap covering the access hole to the fuel pump. Remove the seal and lift the cap to expose the fuel pump.

Step 4: Document the pump connections and disconnect the power line.

Take a picture of the fuel pump connections to ensure proper reassembly. Then, carefully unplug the cable, which is the power line to the pump.

Step 5: Drain the remaining fuel.

Start the engine and wait 5-10 seconds until the engine runs out of fuel and stalls.

Step 6: Disconnect the fuel lines.

Caution: The feeding line (fuel line in the center) is still pressurized and contains almost 1/2 quart of fuel. To minimize the risk of fuel inhalation and spills, collect the fuel into a cup immediately after disconnecting the line. Place towels around the work area to absorb any spills.

To disconnect the fuel lines, push the line and press the tabs on each side with your fingers, and then remove it.

By following these steps, you will successfully disconnect the power line and fuel lines from the fuel pump of your Mercedes ML320, preparing you for the next steps in the fuel pump replacement process.

Removing and replacing the fuel pump

Step 1: Remove the flaps of the rear seats. There are no screws, just tabs. Releasing the tabs is the most challenging step as they break easily.

Step 2: Remove the rear seat bottom covers.

Step 3: Unscrew the rear seats. There are two hex nuts and several torx bolts. Disconnect the SRS cables; one for each seat.

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

Step 5: The 60% seat is very heavy. Just slide it to the location of the 40% seat so that you can work on the driver's side.

Step 6: Fold the floor mat (driver side corner) and you will see a round cap covering the access hole. The cap is attached to the body by sealant only.

Step 7: Remove the seal and lift the cap. You will see the top of the fuel pump. Take a picture to document the alignment of the pump connections.

Step 8: Unplug the cable which is the power line to the pump.

Step 9: Start the engine and wait 5-10 seconds until the engine runs out of fuel and stalls.

Step 10: Disconnect the fuel lines. Push the line, press the tabs on each side with your fingers and remove it. Caution: The fuel line in the centre (feeding line) is still pressurised from the fuel filter which stores almost 1/2 quart of remaining fuel. Collect the fuel into a cup immediately after disconnecting the line. Fuel will come from the line, not from the pump. There will be some fuel spill, so place towels around. This will minimise inhalation of the fuel vapour.

Step 11: Turn the locking ring of the pump counterclockwise and remove it.

Step 12: Lift the fuel pump. It won't come straight up because of the fuel sensor floating arm and secondary intake line (tail-like extension tube). Tilting and turning will be enough. Caution: There is some fuel inside the pump reservoir (the bottom pan). Tilting the pump more than 45 degrees may cause fuel spill. Caution: Be careful not to drop anything inside the tank at this point.

Step 13: Carefully insert the new fuel pump. Check the alignment of the fuel lines and make sure it is the same as the original. Caution: Wrong alignment of the pump may prevent the fuel sensor floating arm from being lifted completely when the tank is full. Therefore, the fuel gauge will never show a full tank.

Step 14: Make sure that the rubber gasket has a tight fit between the pump and the tank. Otherwise, it may cause a leak when the tank is full.

Step 15: Put the locking ring over the pump and draw a line with a pen (mark the initial position).

Step 16: Turn the locking ring clockwise for at least 360 degrees (one full turn). If you have the specific MB tool to remove and install the locking ring, the specification is 65Nm. If you don't have the specific tool, make sure it is tight enough or one full turn. Otherwise, it may cause a leak when the tank is full.

Step 17: Snap the fuel lines in place. Refer to the picture to confirm the feed line which plugs into the centre. Plug in the power cable.

Step 18: Start the engine.

Step 19: Use body sealant to seal the cap.

Step 20: Install everything in reverse order. Do not forget to connect the SRS cable.

Warning: There is a risk of explosion by fuel igniting and a risk of poisoning by inhaling vapour, eye or skin contact with fuel. In order to minimise fuel spill, have a minimum amount of fuel in the tank during the procedure.

Frequently asked questions