Is your Mercedes-Benz difficult to turn, has a battery warning light on the dashboard, the air conditioner stops working, or the engine overheats? Learn how to fix it by following the procedures below.
A common problem with Mercedes-Benz cars is the idler pulley (also known as Guide Pulley or Sheave Pulley), failing as early as 100,000 miles. Changing the idler pulley on a Mercedes-Benz is relatively easy for most DIYers and requires less than two hours.
A bad idler pulley can cause the serpentine belt to come off. Once the belt comes off, you will experience multiple problems if you continue to operate the car.
- Power steering is difficult to turn.
- The alternator stops working and no longer charges the battery.
- Battery warning light on the dashboard
- The Air Conditioner stops working.
- Engine Overheats
- The engine stalls once the battery is drained.
At the early stage, indicating that the idler pulley is failing, you will only hear a squeaky noise from the engine’s front. Inspect the idler pulley if you hear noise from the engine.
The noise can be described as whining. Remove the serpentine belt and check the idler pulley for play or noise by spinning it by hand.
It would be best to replace a bad idler pulley immediately to avoid future problems caused by complete idler pulley failure.
What you will need
- Mercedes Idler Pulley
- Thread Locker
- Female Torx Set
- Torx Socket Set
- Ratchet Wrench
Note that the older models of Mercedes-Benz engines require a Torx Bit Socket. This is common on M112 and M113 engines from 1997 to 2007.
Newer Mercedes-Benz idler pulleys (on M272 and M273 and newer models) require a Female Torx socket. Always verify by inspecting the bolt on the center of your idler pulley.
- Park the Mercedes-Benz in an area where you can work. Changing the idler pulley on the road is possible if it fails while driving. You need to make sure you are working in a safe area.
- Allow the engine to cool down for at least thirty minutes.
- Pull the hood release under the dashboard on the driver’s side.
- Remove the engine cover by lifting it. Locate the idler pulley at the front of the engine.
- Remove the serpentine belt. Use a 17mm socket and ratchet on the tensioner nut to unload the tensioner.
- Use a pin to lock the tensioner in the pre-loaded position. You can use a nail or a 5mm Allen wrench as a pin.
- Slide the serpentine belt off the idler pulley. Removing the serpentine belt completely is unnecessary unless you are replacing it.
- Use a flathead screwdriver to remove the dust cap on the center of the idler pulley. Do NOT discard the dust cap. It needs to be reinstalled.
- Use a T-50 Torx to remove the idler pulley bolt. The bolt is long and requires patience to remove. Some models require a female Torx socket.
- Install the new idler pulley and tighten the bolt to Mercedes-Benz specifications.
- Install the dust cap.
- Turn the idler pulley by hand to make sure it is spinning freely.
- Reinstall the serpentine belt. If the belt is not long enough to slide over the tensioner pulley, ensure it sits properly in all the pulleys.
- Use your 17mm socket and ratchet to move the tensioner upward to remove the locking pin.
- Slowly load the tensioner.
Typical Mercedes-Benz idler pulley bolt torque:
- Newton-meters 35 Nm
- Foot-pounds: 25.81 ft-lb
These torque specs may vary between models. We recommend you verify the correct torque specs by calling your Mercedes-Benz dealer.
- It is recommended (not required) to change the tensioner while you change the idler pulley.
- If your vehicle has a viscous fan, it may need to be removed to access the idler pulley. Common on pre-2000 models.
Below are part numbers for some of the most common Mercedes-Benz idler pulleys.
000 202 09 19
M112 and M113
||A272 202 10 19
M272 and M273
We hope you find the “Mercedes-Benz Idler Pulley Replacement” guide helpful. Check these troubleshooting and repair guides for more help on your Mercedes-Benz.