Mercedes Benz OM642 3.0 Diesel Engine Alternator Replacement

Is your Mercedes-Benz battery not charging, hard to start, and dying when driving it? Learn how to fix the problem by replacing the alternator of your Mercedes-Benz.

This guide provides instructions on changing 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.

Symptoms

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

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Parts

• Alternator OM642
  • See part numbers below.
• Serpentine Belt OM642
  • Not required, but recommended to replace at the same time.

Tools

• E-Torx set
• Torque wrench
• Pry bar
• Penetrating oil
• Screwdriver
• 17mm socket
• 10mm automatic combination wrench

Procedure

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, and Sprinter designed as 320 CDI or 350 BlueTech.

Removal:

1. Park vehicle on level ground.
2. Pull the hood release under the dashboard, open the hood, and ensure the hood support is appropriately secure.
3. If the engine is still hot, let it cool for a while to prevent 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. It would help if you used a 13mm socket to remove the terminal.
5. Remove all the hoses 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 the upper hose separately to the lower hose.
6. Please 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 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; do not forget to put it back.
9. Remove some more components at the side of the alternator if necessary, giving 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 most accessible 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 always to 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.

Installation:

1. Install the new alternator. It will be easy if you have someone to hold the alternator while 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 ensure that the screwdriver supports the alternator while installing one of the bolts on the other hole. Install all the remaining bolts and tighten them 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, and ensure it is sitting correctly on each pulley.
6. Install all the hoses and ensure that the metal clips are correctly 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

Applications

This procedure applies to all Mercedes-Benz equipped with the OM643 diesel engine. Part numbers may vary. Access to the alternator may also vary due to the engine setup 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:

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.

Reference

1. Mercedes Benz Alternator Replacement Cost – repairpal.com
2. Mercedes Benz Alternator Life Span – oklahoma.com
3. Mercedes Benz Alternator Test – youtube.com

We hope you find the Mercedes Benz OM642 3.0 Diesel Engine Alternator Replacement guide helpful. Check these troubleshooting and repair guides for more help on your Mercedes-Benz.