Hi everyone

I am pulling my hair out over an issue with my 2008 ML320 CDI.
I had an alternator fail back in the summer (bearings worn), nothing unexpected as it had done 200,000 miles.
I replaced it and the new one lasted for only 2 months, as it was under warranty I got a replacement and fitted that one.
the replaement lasted 3 weeks.
I have now today fitted another replacement and it lasted all of 1 hour before failing again.

Each time the replaement is fitted I check to make sure it is charging correctly and it shows 14.1V (seems reasonable). Howeer none of them are lasting. I could understand getting a bad one through bad luck... but 3... is there something g that could be breaking these?

with the last one fitted I also changed the battery (just in case) but it was no help.

thanks

 

The big question is, did all of the alternators come from the same place?

How do you know when the alternator has failed?

Are you using the Inst. Cluster to get the 14.1 reading and was it done with or without consumers (radio, blower on, etc.)?

What is the battery reading with the eng. off?

Who installed the alternators?

 

Yep, the alternators came from the same place.
when first installed they provide an nice healthy 14.1 V output (measured with canbus reader, on dash and with voltmeter)

when they fail I get all the abs failure lights, And other warning systems come up as failing on the dash, measure the voltage with a voltmeter and with canbus and it usually shows around 7 V. Restarting doesn't help. I need to manually recharge the battery, but never get 14.1 v again.

the voltage measrements (good and bad) are always taken with as much turned off as possible (no heaters, blowers, radio etc)

the alternators have been installed by a couple of different people.

thanks

 

You are getting ABS codes because voltage has dropped below 11v.

The alternator that lasted one hour might indicate that there is a short someplace. Let me get the diagram. I'll post back.

 

Thanks! I really appreciate the help

 

"Yep, the alternators came from the same place."

Pretty big clue there. New or rebuilt alternators? Brand?

 

They were supposedly new, unknown brand
could all 3 have been bad?

 

Supposedly new and unknown brand. There's your sign.

 

OK, M/B does not supply a wiring diagram for starting and charging, just a functional diagram. But they do show a diagram for U880, N3/9 CDI Cont. Mod.

Go to the end of that diagram and you will find the Alternator G2.Look at the cables coming off it. One goes to the starter M1, one to CDI N3/9 and the last to the Glotime Output Stage N14/3.

Something must be wrong with the wiring to and from the Alt. and you will have to find it somehow.