Accessory belt replacement on Mercedes C-Class w203

Pull the red lever located under the steering wheel. The hood will lift slightly.

Pull the black lever located at the front of the hood to open it completely.

Locate the oil cap.

Please note: The position may vary from one engine to another but the principle will always be the same.

Unscrew the oil cap a quarter turn, then remove it.

Unclip the engine cover by lifting it firmly.

Screw the oil cap back on.

Locate the tensioner pulley.

Locate the spring tensioning port and the tensioner locking hole.

Position the 17 to 12-sided key, and keep the Locking Rod within reach.

Caution: This step requires tensioning the spring, proceed with caution.

By turning the key counterclockwise, tension the spring until the Locking Rod can be inserted into the locking hole. The tensioner is now locked.

Warning: before removing the belt, make a diagram of its path on the different pulleys or take a photo. The belt must be reassembled identically.

With the belt no longer under tension, it can be removed with ease.

This step is optional, it is not mandatory to replace the tensioner roller, but it is nevertheless recommended.

Locate the 2 bolts that hold the tensioner roller in position then unscrew it using the 8 mm wrench

Remove the old tensioner and then install the new one. Tighten the retaining bolts.

Reposition the belt by referring to the diagram or photo.

Re-tensioning: As for step 3, apply tension to the tensioner using the 17 mm wrench. Remove the Allen key which acts as a lock then release gently to tension the belt.

Check carefully that the belt is correctly positioned at the various pulleys.

Caution: It is imperative to check the correct installation of the new belt before starting the engine.

Unscrew the oil cap, it lifts off after turning it a quarter turn.

Clip the engine cover by pressing it firmly.

Screw the oil cap back on.

Close the hood and the operation is complete.