Mercedes-Benz Parts Catalog Mercedes-Benz Accessories Catalog Mercedes-Benz Technical Articles Mercedes-Benz Tech Forums
 
Follow Pelican Parts on Facebook Follow Pelican Parts on Twitter Follow Pelican Parts on Instagram Follow Pelican Parts on YouTube Follow Pelican Parts on Pinterest Follow Pelican Parts on Tumblr
  Search our site:    
View Recent Cars  |   Cart  | Project List | Order Status | Help    
Bookmark and Share

Pelican Technical Article:

Alternator Replacement

Nick Czerula

Time:

3 hours3 hrs

Tab:

$200

Talent:

*****

Tools:

10mm, 13mm, 17mm sockets, E14 inverted Torx socket.

Applicable Models:

Mercedes-Benz W211 (2003-09)

Parts Required:

Alternator, drive belt, idler pulley

Hot Tip:

Work with a cool engine

Performance Gain:

Car will charge properly

Complementary Modification:

Change serpentine belt, idler pulley

A faulty or failing alternator can cause many problems, from a simple discharging of the battery to an engine drivability problem. There are a few signs and tests you can perform to determine if the alternator is the root cause of your problem. If you get lucky, your battery light (charging system indicator) will illuminate to warn you of a possible failure. When the battery light (charging system indicator) is ON, this means a voltage difference has been detected between battery positive (+)constant (terminal 30) and ignition ON circuit (terminal 15), indicating a fault in the charging system.

It is common for an alternator to fail slowly. When this happens your symptoms will be present when the electrical system has the highest load, ie. at night. Driving at night, you may notice the instrument panel lights dim, or the radio or headlights flicker. This is a good indication that the alternator cannot handle the excess load. Another sign of a charging system problem is headlights or radio dim when lowering your window. When the alternator can no longer charge the battery, you may park your vehicle and not be able to start it. Of course, this could be a faulty battery too.

Always check the voltage of your charging system under load. Voltage should be within 13.2: 14.5 volts d/c. To load, have the engine running at idle. Turn on the headlights and HVAC blower motor. Never disconnect a battery cable while engine is running to test alternator. You may cause damage to alternator or other electrical components from the surge in amperage. Before performing any tests of your alternator, charge and test your battery. If the battery is faulty, your alternator tests will not be accurate.

In this article, I'll go over the steps involved with replacing the alternator on Mercedes-Benz models with 6-cylinder engines. Be sure to work with a cool engine and disconnect the battery before beginning. W211 models can come with a few alternator amperage ratings. Be sure that your replacement alternator has the same rating as faulty unit. You can usually find the amperage rating on the alternator housing.

Working in the trunk, disconnect the battery negative cable and cover the battery terminal so the cable does not accidentally come in contact with the terminal. See our tech article on battery replacing for notes on disconnecting and reconnecting the battery.

The alternator on W211 models with a 6-cylinder engine is located on the right side of the engine (red arrow).
Figure 1

The alternator on W211 models with a 6-cylinder engine is located on the right side of the engine (red arrow).

Working at the engine cover (red arrow), pull off the two front sir duct hoses (green arrows).
Figure 2

Working at the engine cover (red arrow), pull off the two front sir duct hoses (green arrows).

To detach the ducts, pull them straight off the engine cover / air filter housing.
Figure 3

To detach the ducts, pull them straight off the engine cover / air filter housing. Then pull the front of the duct out of the radiator support and remove them from the engine. Repeat this step for each duct.

Lift up and remove the front engine cover.
Figure 4

Lift up and remove the front engine cover.

Then, pull the engine cover / air filter housing straight up to remove it.
Figure 5

Then, pull the engine cover / air filter housing straight up to remove it. Four metal clips that grab onto rubber mounts hold on the cover. The front two are shown (red arrows). The rear of the cover has two as well. Once detached, remove the engine cover / air filter housing from the engine.

Locate the accessory drive belt tensioner (red arrow) on the left side of the engine.
Figure 6

Locate the accessory drive belt tensioner (red arrow) on the left side of the engine.

Using a ratchet with a long handle and a 17mm socket, rotate the drive belt tensioner counterclockwise to release tension and slide the belt off the pulleys (red arrow).
Figure 7

Using a ratchet with a long handle and a 17mm socket, rotate the drive belt tensioner counterclockwise to release tension and slide the belt off the pulleys (red arrow). Remove the engine drive belt. See our tech article on engine drive belt replacing for detailed information.

Working at the top of the alternator, remove the E14 bolt (red arrow).
Figure 8

Working at the top of the alternator, remove the E14 bolt (red arrow). Note that both alternator bolts are the same length.

Working at the bottom of the alternator, remove the E14 alternator mounting bolt (red arrows).
Figure 9

Working at the bottom of the alternator, remove the E14 alternator mounting bolt (red arrows). The lower bolt is hidden under a coolant hose. The inset shows a view from under the hose. Note that both alternator bolts are the same length.

Now the alternator can be removed.
Figure 10

Now the alternator can be removed. If it is stuck, lever the alternator away from the engine. Working at the bottom of the alternator, lever the alternator away from the mounting bracket using a pry bar (green arrow). Next, remove the alternator from the mounting bracket by rocking it back and forth while pulling up and off the bracket. Once you wiggle it out of the mounting bracket, flip the alternator over, so the pulley is facing down.

Working at the back of alternator, disconnect the electrical connector (red arrow) by pressing the release tab and pulling the connector straight off.
Figure 11

Working at the back of alternator, disconnect the electrical connector (red arrow) by pressing the release tab and pulling the connector straight off. Then remove the alternator positive (+) cable fastener protective cap (green arrow), pull it straight off to remove (inset). If the protective cap is stuck, use a small flathead screwdriver to gently lever it off. Do not damage it, as you will have to reinstall it later.

Then remove the 13mm alternator positive (+) cable fastener (red arrow).
Figure 12

Then remove the 13mm alternator positive (+) cable fastener (red arrow). Once the fastener is removed, lift the cable and remove it from the alternator.

To remove the alternator, lift it toward the front of the engine with the pulley facing left.
Figure 13

To remove the alternator, lift it toward the front of the engine with the pulley facing left. Then hold the radiator hose of out the way as you lift. Move to the right under the dipstick, and remove it from the engine. W211 models can come with a few alternator amperage ratings. Be sure your replacement alternator has the same rating as the faulty unit. You can usually find the amperage rating on the alternator housing (red arrow). Place the new alternator in the engine compartment and feed it down toward the mounting bracket. Attach the electrical connections to the back of the new alternator and tighten. Install the new alternator in the alternator bracket. Then install the fasteners and tighten. Install the drive belt and check that the belt is properly aligned in the alternator pulley. Then reassemble the remaining items in the reverse order of the removing steps. Connect the battery negative cable. Check the operation of the charging system and alignment of the drive belts.

Bookmark and Share
Comments and Suggestions:
Darin M. Comments: Is this pretty much the same process to remove the alternator in an E55?
August 31, 2016
  Followup from the Pelican Staff: Similar. It should get you done. - Nick at Pelican Parts  
j23 Comments: thanks for info, BUT, i dont see how anyone can get the alternator past the hoses in order to remove it without removing the fan shroud first. As the Mercedes Workshop Instruction Manual says to do. Once the shroud is removed, the hoses can be pushed out of the way enough to get alternator out and new one in. So much easier and less stressful on hoses. Shroud removal only causes minimal coolant loss esp. compared to pulling hoses.

Plus, any tips on torquing nut that holds electrical cable onto alternator would be helpful.

thanks again
May 22, 2016
  Followup from the Pelican Staff: We got it no problem, removing it on an angle as shown in the article. - Nick at Pelican Parts  

  Search our site:    

View Cart & CheckOut | Project List | Order Status |  Help    

 

[Home] [Customer Service] [Shopping Cart] [Project/Wish List]
  [Privacy Statement]  [Contact Us] [About Us] [Shipping] [Careers]

Copyright © Pelican Parts Inc. -    DMCA Registered Agent Contact Page

Page last updated: Mon 12/5/2016 02:43:31 AM