C270 CDi Alternator Warning

[malteser]

Hello Mercedes Gurus. I would like to share current ongoing problem with an annoying issue I have of constant flashing of a warning on the instrument cluster saying: "Alternator/Battery - Visit Workshop" at a rate of about 5 or 6 times a minute and each lasting a few seconds. This vehicle is fitted with a 190Amp Delphi watercooled alternator. When I checked out the charging voltage as well as load tested the battery both were fine. However I still proceeded in replacing the battery and also the alternator (that was some undertaking) to utterly no avail. I have therefore had the car hooked up to STAR and watched the live data for some parameters on the SAM and what we noticed was that the flashing of the error happened concurrently when the state changed on Terminal 61. Searching on the internet I've heard that this input is hooked up to the Field output from the alternator, and therefore my current thinking is that there could be a dodgy connection along this line. I've removed the SAM and all the connectors are very clean and dry, and all fuses in working order. However I haven't got a schematic diagram to identify the alternator wire so that I can do a continuity check. Does anyone have such a schematic or perhaps anyone knows exactly to which plug and pin position on the SAM this wire connects to? Furthermore any advice with this problem? Somebody also told me that these SAMs go loopy? Any comments appreciated.

 

[Steve@Avantgarde]

There is a signal wire on the pack of the alternator, they usually break around where it loops around the turbo. Check that wire, there will be a break somewhere.

 

[malteser]

I really would appreciate if anyone has access to this vehicle's wiring diagram to get a schematic for the two thin wires which come out of the voltage regulator at the back of the Alternator. They must go somewhere, is it the SAM and what plug and pin position?

 

[Steve@Avantgarde]

They do go to the SAM but they usually break around the turbo area. They are in black sheathing. Peel it back, you will find the break, its a common issue.

 

[Westheath]

Hmm that's strange, just had one in today with a broken wire,
sheathing was intact and wire casing undamaged,
just the copper wire inside deteriorated and broken.

So it might look ok but pull on the connector and see if the sheathing/casing breaks along the cable length.

 

[malteser]

@steve: do you have a charity you support? I'd be happy to make a donation. Your advice was spot on. Found sheathing as well as insulation to the Field Sense wire eaten into through the rubbing agains the turbo bracket resulting in exposed copper which was shorting to ground. Thanks for the hint.

 

[karle]

They do go to the SAM but they usually break around the turbo area. They are in black sheathing. Peel it back, you will find the break, its a common issue.

Steve, you were spot on with your cure, asked my garage to run a new wire and sure enough problem solved, thanks for this tip, being driving me round the wall trying to find the problem

 

[Steve@Avantgarde]

@steve: do you have a charity you support? I'd be happy to make a donation. Your advice was spot on. Found sheathing as well as insulation to the Field Sense wire eaten into through the rubbing agains the turbo bracket resulting in exposed copper which was shorting to ground. Thanks for the hint.

A lovely gesture, anything that goes towards cancer cure or arthritis care is fine by me.

 

[Pierrew252]

I have a 2006 C320 Cdi with 405,000 km and it has the same problem. New battery and charger did not fix the problem.
Will the suggested fix apply to this model as well?
Regards
Pierrew252

 

[mioba]

Yes if the wire is worn through. you need to check obviously.