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This guide provides instructions on how to change the alternator on a Mercedes Benz OM642 3.0L V6 diesel engine found on R - Class, GL, ML, E- Class, and Sprinters.

Replacing the alternator on a Mercedes Benz 3.0L V6 engine is relativity easy and takes about two hours. 

Table of Contents


Common symptoms indicating a problem with your Mercedes Benz alternator include:

  • The battery light stays on
  • A warning message in the dash
  • The battery won't charge, Dead battery
  • Car dies when driving
  • Instrument cluster lights are dim
  • Whining and growling noise
  • Having trouble starting the engine

What you will need




Follow these steps to change the alternator on any Mercedes-Benz with the 3.0L V6 diesel engine found on E-Class, R-Class, ML-Class, GL-Class, Sprinter designed as 320 CDI or 350 BlueTech.


  1. Park vehicle on level ground.
  2. Pull the hood release under the dashboard and open the hood and make sure that the hood support is properly secure. 
  3. If the engine is still hot, let it cool for a while to prevent any unnecessary accidents.
  4. The location of the battery is right under the passenger seat, lift the floor mat, and you will see the battery terminal bolted to the frame. You need to use a 13mm socket to remove the terminal.
  5. Remove all the hose that is blocking the serpentine belt, and to do that, use an E-12 Torx to remove the bolts of the upper hose. Use a screwdriver to slide the metal clip on the hose tab, then pull separate the upper hose to the lower hose.
  6. Pay attention to how the serpentine belt is routed; there may be a chance you might forget it, so I suggest you take a photo or maybe draw the serpentine belt routing pattern.
  7. Place the 17mm socket in the tensioner bolt; you can use a long handle so it will be easy to push the handle down counterclockwise, then slide the serpentine belt out.
  8. Remove the ground wire from the alternator to the chassis; just do not forget to put it back.
  9. Remove some more components at the side of the alternator if necessary, so it will give you more room to use when pulling the alternator out.
  10. Remove the alternator bolts using the 10mm automatic combination wrench, this will help speed up the procedure, but if you don't have one, you can still use the E12 socket wrench.
  11. Start unscrewing the top bolts and remove then go under the vehicle. It's the easiest access to the bolts.
  12. Remove the remaining two bolts in the bottom part of the alternator then you will see the positive terminal use 13mm to remove the nut and unplug the connector.                                                                                                                                                                                                                       NOTE: Remember to always disconnect the negative battery terminal because the alternator terminal is always live; neglecting that procedure may cause harm to the technician and also to the vehicle's electrical components. Pull the alternator up; you might need to push some hoses to take the alternator out. 


  1. Install the new alternator. It will be easy if you have someone to hold the alternator while you are installing the alternator bolts, but if not, it will be ok. 
  2. First, install the positive terminal and the connector of the alternator.
  3. Align the alternator to its proper position, install a screwdriver in one of the holes and make sure that the screwdriver is supporting the alternator while you are installing one of the bolts on the other hole. Install all the remaining bolts and tighten it to the specified torque.
  4. Install the ground wire from the alternator to the chassis.
  5. Install the new serpentine belt to its original routing position, make sure that it is sitting properly to each pulley.
  6. Install all the hoses and make sure that the metal clips are properly seated, install the bolts of the upper hose, and tighten them to the specified torque.
  7. Reconnect the battery terminal.
  8. Start the engine.
  9. Check on the cluster for any warning lights regarding the repair, and you can also use a multimeter to check if the battery is charging while the engine is running, you should be getting 14V to 14.8V


This procedure applies to all Mercedes-Benz equipped with the OM643 diesel engine. Part numbers may vary. Getting access to the alternator may vary as well due to the setup of the engine in the engine bay.

Examples where these instructions apply: 

  • MERCEDES E-CLASS 11-13 212 Type, Sdn, E350, diesel
  • MERCEDES GL CLASS 09 164 Type, GL320
  • MERCEDES GL CLASS 10-12 164 Type, GL350
  • MERCEDES ML SERIES 10-11 164 Type, ML350, diesel (220 amp, Bosch manufactured)
  • MERCEDES S-CLASS 12-13 221 Type, S350
  • MERCEDES R-CLASS 09 251 Type, R320
  • MERCEDES R-CLASS 10-12 251 Type, (R350), diesel
  • MERCEDES R-CLASS 13 251 Type, (R350, diesel)

Part Numbers

Possible part numbers include:

LESTER 11309
MERCEDES BENZ 642-154-03-02
MERCEDES BENZ 642-154-05-02
MERCEDES BENZ A642-154-03-02
MERCEDES BENZ A642-154-05-02
VALEO 2543290
VALEO 439583
VALEO 440053

This is not a complete list of part numbers.

Frequently Ask Questions 

How much does it cost to replace a Mercedes Benz alternator?

  • The average cost to replace a Mercedes-Benz alternator is between $550 and $700. Labor costs are estimated between $165 and $250, while parts are priced at $350. If you replace it yourself, expect to pay about $150. 

How long does a Mercedes Benz Alternator last?

  • The average life span of an alternator is about seven years or 100,000 to 150,000 miles. It depends on the quality of the parts and how many electronic components are installed.


  1. Mercedes Benz Alternator Replacement Cost -

  2. Mercedes Benz Alternator Life Span -

  3. Mercedes Benz Alternator Test -

Mercedes Benz OM642 3.0 Diesel Engine Alternator Replacement This guide provides instructions on how to change the alternator on a Mercedes Benz OM642 3.0L V6 diesel engine found on R - Class, GL, ML, E- Class, and Sprinters.

Replacing the alternator on a Mercedes Benz 3.0L V6 engine is relativity easy and takes about two hours.