How to Replace a Serpentine Belt on a Mercedes S430

1. Check to see whether there is a routing diagram for the belt under the hood of the car. If there isn't one, draw one. This diagram is to guide you when installing the new belt.
2. Place your socket wrench on the bolt end of the tensioner pulley. The tensioner pulley is in the upper center of the engine compartment and has a hex-bolt head protruding from its center. Apply downward pressure to rotate the pulley and relieve the tension on the belt.
3. Remove the belt from the pulleys. There will be six of them.
4. Install the new belt on the pathway as shown on the diagram, saving the tensioner pulley for last. Apply pressure to the pulley bolt to rotate the pulley again and slip the belt over it. Release the pulley and there will be tension on the belt. The tension in the belt is set automatically by releasing the tensioner pulley.