Replacing Fuel Tank Vent Valve In Mercedes-Benz W203

Replacing the fuel tank vent valve on your MB W203 is a relatively straightforward task that can be accomplished in less than an hour. The fuel tank vent valve, also known as the purge valve, is part of your car's evaporative emissions control system. It plays a crucial role in capturing and recycling fuel vapours, particularly during fill-ups, by directing them back to the engine to be burned once specific performance parameters are met. A faulty purge valve can cause issues such as a failed SMOG test, error codes, and even impact fuel efficiency. To replace the valve, you'll need a flathead screwdriver and replacement hose clamps, as the factory clamps will likely be destroyed during the process. The procedure involves carefully removing the valve, ensuring proper hose connections, and reassembling the components in the reverse order.

Locating the valve

To locate the fuel tank vent valve, you will need to look under the bonnet, on the front right side of the engine block (driver's side) in a vertical position. You will be looking at the top of the valve.

The purge valve is located under the left side air intake. To access it, you will need to remove the intake by compressing it back off the air filter cover and then sliding it off the plastic duct on the front trim piece. With the duct removed, you will be able to see the purge valve. It sits in a metal bracket with a rubber grommet.

The fuel tank breather valve is located under the intake plenum in the valley between bank 1 and 2 valve covers, and is attached to the idle control valve. To access it, you will need to remove the rear suction hood, front suction hood, air box, coolant reservoir, intake plenum, and intake elbow.

The charcoal canister shut-off valve is located at the back of the car, near the spare wheel.

Disconnecting the power

Firstly, locate the valve. It is situated on the front right side of the engine block (driver's side) in a vertical position. You will be looking at the top of the valve.

Now, disconnect the power. You can do this by sliding the silver 'locking' wire forward. Once unlocked, pull the power line straight up.

At this stage, the valve is still held in place by a rubber jacket that sits on a thin piece of metal. You can now carefully pull the valve up vertically, wiggling it back and forth to dislodge it. You will then have some 'play' in the valve and be able to move it around a little.

Note the position of the rubber jacket as you will need to place the new valve jacket in the same position.

Removing the valve

The first step in removing the fuel tank vent valve is to locate the valve itself. This is found on the front right side of the engine block (driver's side) in a vertical position.

Next, disconnect the power by sliding the silver 'locking' wire forward. You can then pull straight up to disconnect the power line.

The valve is held in place by a rubber jacket that slides onto a thin piece of metal. Carefully pull the valve up vertically and wiggle it back and forth to dislodge it from its position. Note the position of the rubber jacket, as you will need to place the new valve in the same position.

Now, disconnect the rubber fuel hose on the side of the valve. This is the easier of the two hoses to disconnect. You will need to push down hard on the 'C' clamp and pull the hose straight back.

The bottom hose is more difficult to access, especially if you have large hands. You will need to manoeuvre your hand underneath the valve and clamp down on the grip where the hose meets the valve. Keep your hand locked in this position and then twist the whole valve counter-clockwise while pulling upwards. After some force and revolutions, the valve will dislodge.

Disconnecting the rubber fuel hose

Step 1: First, locate the rubber fuel hose on the side of the valve. It is held in place by a "C" clamp.

Step 2: Push down hard on the "C" clamp and pull the hose straight back. This will disconnect the hose from the valve.

Step 3: Now, locate the rubber fuel hose on the bottom of the valve. This one is more difficult to access, especially if you have large hands.

Step 4: Maneuver your non-dominant hand underneath the valve and clamp down your grip where the hose meets the valve. Keep your hand locked in this position.

Step 5: With your dominant hand, twist the whole valve counterclockwise while simultaneously pulling upwards on the valve. After some force and revolutions, the valve will dislodge.

By following these steps, you will successfully disconnect the rubber fuel hose from the fuel tank vent valve.

Reattaching the new valve

Now that you have removed the old valve, it's time to install the new one. This process is essentially the reverse of the removal process.

First, carefully put a very thin layer of Vaseline on the new valve where you will be sliding on the bottom hose. Be sure to only apply Vaseline to the tip and do not get it inside the entrance hole. Then, push the bottom hose onto the new valve.

Next, connect the side hose by pushing down on the clamp and pushing the connections into place. You should hear a "click" once it is engaged.

Now, slide the rubber jacket back onto the piece of metal that holds the valve in place.

Then, connect the power line and click down the "locking" wire.

Finally, reset your code. You can do this by driving to your nearest O'Reilly Auto Parts store and "renting" out (it's actually free) their OBDII Code reader. Autozone can no longer legally reset codes, though you might be able to get an employee to hook you up anyhow. Your code will eventually clear itself, but you may not want to wait.

Frequently asked questions