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Mercedes-Benz E-Class and E-Class AMG: Why is My Serpentine Belt Squeaking?

That's not a cricket hiding in your engine, but it's just as annoying as one. This guide will show you how to get rid of that high pitched squeak.

By Jared Hammond - June 18, 2015
Contributors: paulv

This article applies to the Mercedes-Benz E-Class and E-Class AMG w211 (2002-2009).

Many Mercedes-Benz owners suffer from the malady of a squeaky serpentine belt. Usually it occurs whenever you first start a cold engine, and it results in a very irritating high pitched squeak. This article will go through the three things you can change to solve this problem. Check out the information below to learn more.

Step 1 – Check the upper idler pulley

The upper idler pulley is the top-most pulley attached to your serpentine belt. Dealerships often check this part first because it's prone to failure. To check if it's the cause, just try removing it and putting it back in. Sometimes, just re-seating the pulley is enough. You can also replace the upper idler pulley for between $15 to $30. Here's how you do it:

  • Loosen the tensioner bolt to loosen the serpentine belt.
  • Slip the belt off the upper idler pulley.
  • Pry off the dust cover on the upper idler pulley.
  • Remove the bolt in the center of the pulley, and remove the pulley itself.
  • Install the upper idler pulley and torque the bolt 15 lb-ft.
  • Reattach the serpentine belt, and then tighten the tensioner bolt.
Figure 1. Upper idler pulley.

Step 2 – Replace the tensioner pulley

If the upper idler pulley isn't at fault, then it's most likely that the tensioner itself is going bad. A replacement tensioner will cost between $115 to $150. Here is how you replace the tensioner pulley:

  • Loosen the tensioner bolt until it is loosened all the way, and there is zero tension on the belt.
  • Insert a metal pin or nail into the small hole in the side of the tensioner pulley. This will lock down the internal mechanism.
  • Slip the serpentine belt off the tensioner pulley.
  • Remove the mounting bolts on either side of the pulley.
  • Remove the tensioner pulley.
  • Install the new tensioner pulley, and then torque the mounting bolts to 18 lbs-ft.
Figure 2. Tensioner pulley.

Step 3 – Replace the serpentine belt

In most cases it is either of the above two components that cause the squeak. But if the serpentine belt is cracked or damaged, it could also cause some noise and eventually lead to trouble starting the car. In the unlikely circumstance that you have to replace the serpentine belt, it will cost you between $30 to $50. Here is how you replace the serpentine belt:

  • Loosen the tensioner bolt until there is zero tension in the serpentine belt.
  • Pull the serpentine belt out from all of the pulleys.
  • Wrap the new serpentine belt around the pulleys.
  • Make sure that the belt is properly seated into the grooves of each pulley.
  • Tighten the tensioner bolt until the serpentine belt is no longer loose.
Figure 3. Follow this diagram when installing the serpentine belt.

Pro Tip

If you plan on replacing all three components, it's recommended you remove the serpentine belt first and install it last.

(Related Article: How to Replace Serpentine Belt - MBWorld.org)

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