Cruising down the fwy, ABS light comes first, next ASR light comes on, 1 minute later engine dies. No charge in the battery. The battery icon never came on as a warning of an electrical charging system malfunction. Battery charged, and car was able to be driven back home, but the fellow at the gas station told me the charging system was not working. Since there was no indication of a charging system trouble, am I looking at more than just an alternator replacement? Even with the battery charged, no icons cone on with ignition on, except for the check engine light only. Please help. Tks.

What model? Year? If it is the original alternator, probably needs a new set of brushes/regulator. Do a search on the subject.

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J.H.
'86 300E

I recently suffered alternator failure in my 420SEL. I guess 14 years and 180,000 miles was about all it could handle. While my car never died on me, had I let it go any longer it may have. I had similar symptoms, ABS light would come on and off, etc. Also, my charge light flickered on and off. The radio would come in and out and my headlights dimmed considerably. A new Alternator was like 400 bucks. Fortunately my mechanic was able to change the voltage regulator and alternator brushes (sold together for $67) that fixed things fine. On most other cars the alternator is a one piece deal made to be thrown out every few years. I'm glad Mercedes had the foresight to make ours easily rebuildable. I would have things checked out however, since your charge light never came on. There are ways to check it such as measuring the charge of the battery. I am no expert at this, but I was part of a post a few weeks ago and got some good advice. I will see if I can find it for you.

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Jason Priest
1999 E430
1995 E420 - retired
1986 420SEL - retired

Look for the post "300SD Battery or alternator??" started by bhatt. There are some good ideas in there.

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Jason Priest
1999 E430
1995 E420 - retired
1986 420SEL - retired

I forgot to mention 300E 91, 3 liter engine. 164K miles and was working fine all these years until this December (broken air injection pump 2 weeks ago. The car runs OK with the battery charged but when I turn the ignition no lights are present on dashboard. A series of clicks occur afdter I turn the ignition off: 1 at a small relay in the drivers side relay bo, another next to the battry and a sound that appears to be similar to AC clutch disengagement.BTW the light sequence before shutdown ABS-SRS-death........no battery icon warning......it seems I can rebuild this unit? parts? tks for the repply.

Just for piece of mind let me tell you how your warning light works.

When the key is turned on power goes through the light to one of the brushes in the alternator. It proceeds through the rotating field through the other brush to ground.

The alternator acts as a ground and the light lights. Once the engine runs and the alternator spins this small current energizes the charging process. There is from that time on power from feed diodes to the same brush. This causes the light to have power on both sides so it no longer lights.

It only takes the potential to charge to rid the light. It makes no judgement on capability. Unfortunately its a very poor determinant of the charging systems ability to KEEP up. Once the battery gets below 9v the control units start shutting down.

This is a remnant of simple systems and surely will be replaced with the coming 40v systems. It would be nice if the car manufacturers could put in system status warnings, I'm sure they will.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Thank you Stevebf for that reply. This forum just works great, thanks to all. So it seems that:
Alternator brushes are shot and I have two options:
a)if it is rebuildable, then replace the brush/regulator combo as a unit bought from??
b)replace the alternator as a unit, either rebuilt or new (car is a 91300E @ 164K)
if option a), can I replace the dides/brushes/regulator unit while the alternator is still in the car?
Thank you all again.

Get a quote from the parts shop on this site. I have heard of people changing the brushes and regulator without removing the alternator, but they told me when they did mine it made it easier to take the alternator out as some of the screws were a little rusty and tough to get at. I think that will be the toughest part of this job. Given the age of the car I would not be surpirsed if maybe some are siezed up, but you may get lucky.

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Jason Priest
1999 E430
1995 E420 - retired
1986 420SEL - retired

Adam,
You DO NOT have to remove the alternator. Remove two screws from the back of the alternator, pull old regulator/brushes out (they come together, as a unit), put new one in, screw it back in. You are done. Five minutes max. PartsShop should have it. Around $30. This is a DIY job.

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J.H.
'86 300E

Thanks again. An oil leak was the culprit here it goes: I have a small leak at the corner of the upper front cover, not much but it trickles down to the alternator area. Oil accumulated together with graphite powder from the brushes, causing one to brush to stop adjusting automally as it was wearing down, and judging by the collector ring discoloration may have been for a while. It opened and that caused the battery to run down. I guess the sequence of lights ABS - SRS - check engine - death (all sequentially within one minute or less)is a way of knowing of the engine's impending shutdown. Pulled the brush holder from the bottom (no need to remove the alt--great) Cleaned the contacts, disconnected the battery, car still runs which means it is charging, next I am going to replace the part (3 minute job -DIY). What to learn: upon startup look at your lights (I think I was not looking for a while since the brushes may have been opened for a day or two)for a half second, if they are not on the brushes are opened, if you just turn the key quickly, like I was doing, you will miss this problem since as Steve mentioned the indicator really does not do a proper job.
Thanks to Steve and Mr. Hidalgo.
Happy New Year!