marcmayer

Hi - The red battery light came on and my car was diagnosed with a bad voltage regulator. I've purchased a new one which mounts to the back of the alternator under a plastic cover.

Question: Can you access the rear of the alternator from under the car to replace the voltage regulator, or do I have to pull the alternator? Is the best way to pull the alternator from above or below?

Plutoe

To not remove the alternator you then have to remove the oil filler tube to remove the VR cover--that's a *****--my suggestion is remove the alternator and change the regulator!!

marcmayer

Thanks. So can be done in place, but not the best approach. Best way to remove alternator -from top of engine or from below?

DaveW68

How many miles on your car? It might be better to just replace the entire alternator with a rebuilt one. The brushes on all alternators wear out over time, thus rendering them ineffective.

marcmayer

Is this true on 4matic? Filler tube is related to tear of engine on 4mstics, but something else may be in way.

marcmayer

In the Bosch alternator the voltage regulator includes new brushes.

alx

the job is easy, but requires attention. you are better off removing the alternator and servicing it on a bench with plenty of space and light around.

marcmayer

I pulled the alternator and replaced the voltage regulator. Most of the job was easily accomplished from the top, but 2 of the mounting bolts - alternator to engine - I could only get to from the bottom - so I had to remove front bottom cover. Alternator can only be pulled from top. To make room to remove it, I had to pull the electric radiator fan (wiring connector + 2 clips) and to make room to remove the fan, I had to remove the top coolant pipe (1 bolt, 2 clips, be prepared to catch spilled coolant) and the top cover (metal plate over radiator with hood latches attached - lots of 10mm bolts).

MBNUT1

Love seeing guys who aren't afraid to wrench on their S Class.

marcmayer

FWIW - the Mercedes voltage regulator 0031546906 for the high output alternator included a Bosch voltage regulator F00M346081 and 7 screws (4 for regulator, 3 for cover). Local dealership asked $160 for part - not in stock. Online dealer sold it for $95 with same delivery date. Just found the Bosch part for sale at Summit Racing for $30 - don't know if it includes the screws. http://www.summitracing.com/parts/bch-f00m346081

mercedesbenzs55

This is where I'm at.

If the Alternator is not working properly. I will buy the voltage regulator. As its not draining batteries but isn't putting out the correct output.

marcmayer

Testing while on the car may be the only option.

I had mine tested at local auto parts shop (OReilly)for free on the car. Their diagnosis machine said voltage regulator bad / diodes good.

I then tried to get the alternator tested (off the car) and none of their systems could test it off the car. Tried multiple shops.

mercedesbenzs55

Marc, is this all that is needed to redo the alternators voltage regulator?

http://www.summitracing.com/parts/bch-f00m346081

marcmayer

There is very little that can go wrong inside an alternator:

1. Bearings - if it spins freely/quietly not an issue;
2. Diodes - convert alternators AC output to DC;
3. Brushes - pick up voltage from spinning assembly; and
4. Voltage control

The Bosch part fixes 3 and 4. An on-car test should tell you if the problem is the diodes (which I don't think are available as a separate part).





The screws that hold the voltage regulator to the alternator are also carry electricity so they should be clean/rust free for the best possible contact. If the old ones are clean they should be fine to reuse.

marcmayer

Note that there are 2 alternators available for our cars - a 180 amp and a 220 amp model with different voltage regulators. You can call a dealer with your VIN to make sure which one you have or do what I do and use epc.startekinfo.com. Its the official MB parts catalog same as the dealers use. You can subscribe for a year at a time for free (although they ask for a credit card to verify ID). Enter your VIN and you can get the correct part numbers for YOUR car.

marcmayer

I take it back - looks like they went from free to $75/year. Ouch

mercedesbenzs55

Thanks marc! God, I love this forum!

My Amp is 220v. Is the parts kit universal for both 180 and 220v?

Looks like summit is on back order for this item.

marcmayer

No - different regulator and parts I think. The parts I used are for the 220 amp model (not volts) like you have.

mercedesbenzs55

Oops,I ment 22amp(it says 220 on the black cover in the rear of the alternator.)

Sorry, I don't know much about electrical systems.

DaveW68

And this is why you need a trained professional to properly diagnose the issues with your car and let them handle the repairs.

mercedesbenzs55

Ill let them diagnose, but I can handle the repairs.

DaveW68

OK....step 1 complete: finally recognizing that you cannot diagnosis all of the problems with your car.

Step 2: TBD