Battery/Alternator/Computer malfunction - which is it?!

[patc57]

Hi,

Here's an annoyingly long story...

(I have a UK '05 SLK 55)
About a week ago, Tracker started calling me every time I got in the car to tell me they had detected a movement. Each time it did, I was actually driving the car, so had to select the option along the lines of "I can't explain why this has happened". It seemed to me it thought the car had been moved without the engine running... but the engine was running!

Then today while driving along normally the COMAND system suddenly tells me the battery voltage is too low and that it will turn off in 10 minutes. Interestingly the message included the words: "Please start the engine" - but it was on. Stupidly I thought it needed a kicking so turned the engine off and attempted to start it again, only to get a dreaded 'click' instead of it actually starting. The dash electrics seemed to be ok and there was no other battery warning light lit.

So I got the AA out who jump started the car directly to the battery and hooked up a volt meter. He diagnosed that the alternator must be shot because the voltage was sticking at about 12.2v with the engine running, not what they considered normal for a running car (they expected 13-16v with the alternator on). I then phoned Mercedes who sent out an out-of-hours technician contracted by mercedes-assist. They hooked up a powerpack to the alternative jump start point to the left of the engine and the car started first time.

Weirdly then, with the powerpack off, the car was able to turn over and stop and start fine. We ran all the electrics with the engine running, including COMAND, the rear heated windscreen, the headlights on full beam etc... and it seemed fine, so seemed to rule out the alternator. Scratching his head, the recovery guy seemed to think everything was fine again so he left and I took the car for a drive thinking I might get some charge in the battery.

About 10 minutes into the journey the same warning came up on COMAND about the battery voltage and this time also the power steering, BAS and ESP decided to go off. Got it home and same as before - click and no engine turnover.

Merc are about to recover the car and it'll be taken to the dealership ready for proper diagnosis and repair. Annoyingly the warranty expired in January...

Just wondered if anyone else has come across this so I can go in armed with some info in case they try and fleece me... could it just be a dodgy battery?

Thanks so much for any advice...

Pat

[lee7758]

I think that is not just the alternator, and the battery problem! There should be some problem withe the computer system! I think You should let the MB dealer to have a detail check for you!!

[lucky6600]

I have never heard this before.
Please keep us posted ....