W203 C240 strange warning message

[alancolvin]

I have a W203 C240 with 55,000 miles on the clock.

I am getting a warning message, accompanied by a picture of the battery, telling me:

'UNDERVOLTAGE - CONSUMER DEFECTIVE!'

The handbook merely repeats the message, without any explannation.

Does anyone know what this message means, and what should be done to recitfy the problem?

I would really appreciate your help.

 

[colechelle]

that is telling you that your battery voltage is below the min mark ie low voltage and amp low, poss that the alternator isnt charging, wondering if your car still has battery recall which hasnt been done, i know currantly there is a recall on some alternators due to regulatars defective, if you have a muti-meter see what voltage the battery is cold then start and see if its charging, should be round 13.50 volt...

 

[alancolvin]

Thanks, Colechelle, I'll give it a try, and I'll aslo check if there is a relevant recall which MB have omitted to tell me about

 

[robbo]

Alan,

From my conversation with the dealer about the recall, yours won't be subject to recall as it is an early model like mine, and has a different alternator to the later models.

Thanks for the information btw. depressing reading I must say.

 

[alancolvin]

Sadly, I now know the meaning of this warning message. It means that some system which consumes electricity is faulty.

My MB dealer firstly wrongly diagnosed the problem as a faulty battery cell dragging down the alternator voltage. I was advised to fit a replacement battery, which I did. (Costco sell Bosch batteries for £51, way below MB prices)

Alas that was not the end of the matter.

After fitting the new battery, many of the car's electrical functions had died (no wipers, indicators, fuel gauge, boot release etc.)

The MB dealer's second, and this time correct, diagnosis was that the rear SAM module had burnt out, taking with it the voltage control unit built in to the alternator.

SAM = Signal Acqusition and Allocation module - an expensive electrical gubbins, liberally populated with fuses and relays, located behind the N/S boot lining, which controls many of the car's electrical and elctronic systems.

The result? A new alternator and SAM module - total cost, even with a discount on the parts and labour from an unusually understanding MB dealer, a staggering £850

Very upsetting!

 

[robbo]

hmmm.

Did you repace the battery yourself? I know of someone who disconnected their battery on a W203 and when reconnecting found the same problems as you, wipers, indicators etc. were not working. They took it to the dealer and it transpired that the SAM module had burnt out when the battery was reconnected. This is a well known thing apparently.

There is a distinct possiblity here that the dealer was correct in his initial diagnosis and the SAM module damage was self inflicted (when the new battery was connected).

Sorry to bring you potentially bad news!

 

[alancolvin]

Yes, I did replace the battery myself, but only after taking the precaution of running through the procedure set out in the handbook with my dealer's electrical technician, who confirmed that this was the correct way to do it, and that there should be no problems by so doing.

His only concern was to make sure I knew how to reset the sunroof, windows and ESP systems, again by following the procedures set out in the handbook.

I have since had the original battery re-tested - it has no faulty cells or any other defects.

When I challanged my dealer about anything I could have done to cause the problems by changing the battery, he told me that the only way to cause damage was to correct the battery with the positive and negative terminals reversed (which of course they were not). He was adamant that the original cause was a failed SAM, which in turn took out the alternator's voltage control system.

However, I would be most grateful if you can cite any concrete evidence that changing the battery (assuming correct sequencing of removing and reconnecting the leads) can damage the SAM, I will take up the matter with MB and seek some redress.

If the battery change can cause damage, I would like to understand what additional measures need to be taken to ensure that SAM damage does not occur. If these are not covered by the procedure laid down in the handbook, than any DIY battery changer has a valid case against MB.

 

[robbo]

Its a guy called mobeyone on the 'other' forum (mbclub.co.uk) There's a thread about it. I wont post the link here though.

Perhaps you could contact him directly by PM.