Electrical Gremlin / Flat Battery

[Brian Davey]

Complete newbie on the site, first Mercedes I have owned (since February this year). C200K Elegance, 2008, 55K miles.

Have travelled several thousand miles without any trouble. Last Monday morning, car was totally dead. Had to open driver’s door with the emergency key. Turned ignition, nothing, no power at all, dead, instrumentation blank, no sounds of starter motor trying to turn.

Noticed, strangely, that the rear light clusters were both lit - but no front lights showing. Light switch was set at 0 and stalk in central position. I had auto fold door mirrors option and courtesy lights on option set before fail.

Suspected battery had died and needed replacement. Called out RAC who tested battery and alternator, both tested ok. Got car going again, noticed that door mirrors were folding in but not extending when unlocking the car.

Took car to auto electrician who tested rear light wiring and checked for any water leaks around the electrics but found none.

Can anyone shed any light on the problem, notably rear light clusters being illuminated when battery is flat (and likely causing power drain)??

 

[LostKiwi]

How did you restart it?

 

[John Laidlaw]

I’m fearing the answer already!

 

[Brian Davey]

The RAC man had a power pack - wrong answer??

 

[Botus]

if its all back to normal (except mirrors forgot how to work) this doesn't sound much like a battery issue to me, particularly where you wrote that the rear lights were on with a dead battery - so it wasn't dead - but the car was having a moment ?

SAM issue ? (signal acquisition module) my frowned on name (but easiest way to get your head round what it does) is to think if it as a "posh fuse box" containing a programmable brain. known to give up and make odd things misbehave

 

[Brian Davey]

Thanks for the fast responses. Yes, Botus, car acted as dead but rear lights were illuminated so it wasn’t totally dead..... weirdest thing.
So, yes all back to normal - but without knowing the root cause I am concerned about it simply doing the same again and wondered if the weird rear lights issue had happened to anyone else.

 

[Botus]

not sure which models but there are issues on some with rear light wiring melting or something...
SAM issues are quite frequent

its possible the battery is worn out and as it got low voltage the car got its self confused
A good AGM can do quite some age if the car is used regularly with long runs it might to 10 to 12 years, replaced with a cheap average one the next might do 3 years

 

[Brian Davey]

Thanks Botus. The auto electrician checked the wiring in the rear lights (as he said that was an issue on some cars) but reported that was fine. Sounds like a new battery is the best course of action. Will arrange that next week.

Thanks again.

 

[Botus]

contact Mercedes grangemouth (stating this forum) they do exceptional pricing on batteries and get it sent quick for £5

 

[Flyinspanner]

That, or look at GSF or Eurocarparts (often have 50 - 60% discount codes) don’t go for a ‘cheap’ brand, get Bosch etc.

 

[John Laidlaw]

The RAC man had a power pack - wrong answer??

Nope the fact that the RAC man HAD a powerpack was the worry, shouldn’t be let loose with them especially near Mercs!

 

[daibevan]

That, or look at GSF or Eurocarparts (often have 50 - 60% discount codes) don’t go for a ‘cheap’ brand, get Bosch etc.

Or Tayna batteries on line, often have offers.

 

[EmilysDad]

Nope the fact that the RAC man HAD a powerpack was the worry, shouldn’t be let loose with them especially near Mercs!

Merecedes used one on my car after they'd flattened my battery .... a Merc's only a car .... they're no more special than any other car. What would you like your recovery man to do if he turns up to you at the airport car park after you been & holiday & return to a flat battery?

 

[John Laidlaw]

Merecedes used one on my car after they'd flattened my battery .... a Merc's only a car .... they're no more special than any other car. What would you like your recovery man to do if he turns up to you at the airport car park after you been & holiday & return to a flat battery?

Walk
The equipment isn’t the issue it’s those who wield it sometimes - had personal unpleasant experience of this!

 

[LostKiwi]

Some MBs are very sensitive to voltage spikes when connecting external power sources. R129s for example have a habit of destroying the roof control module - slightly annoying at £1000 for a new one...
A basic precaution is to ensure as many modules are powered off at connection time as possible and ensure headlights are turned on - the headlights will drain the spike.

 

[EmilysDad]

Some MBs are very sensitive to voltage spikes when connecting external power sources. R129s for example have a habit of destroying the roof control module - slightly annoying at £1000 for a new one...
A basic precaution is to ensure as many modules are powered off at connection time as possible and ensure headlights are turned on - the headlights will drain the spike.

Obviously a p poor design then if a car is incapable of something as basic & routine as a jump start