W202 C43 AMG Battery drain issue.

[Pedro86]

Hi Guys, Right i left my C43 parked up for four days came back to it with a dead battery. The battery only had 3 volts so i assumed it wasn't worth charging. I fitted a new battery started the car fine drove it around the block and parked her up. The next day i went to use the car again, guess what same thing dead battery. This time i jump start it and take it to the garage.

We did a drain test on the car both locked and unlocked we only had a reading of 0.3 amp which im told is well within tolerance. We suspected a possible fault with the new battery re-charged it, Left the car locked overnight again in the garage and its drained again!

Are you guys aware of any common faults or aux systems that are automated?

 

[Dec]

What year is the car also is your car alarm working properly?

Dec

 

[AL3X]

My w204 just had this issue which turned out to be the rear SAM, however mine was drawing a lot more when locked...

I hope for your sake it's not this as mine just cost £720 from Merc, at trade!

A word of warning though, its not good to jump these cars as that alone can kill SAM units etc!

 

[Pedro86]

What year is the car also is your car alarm working properly?

Dec

Its a 99' and the alarm was working fine last week not to say it hasnt broken now. If the alarm was faulty wouldnt it be draining all the time?

 

[Ted]

.3 amp amp drain on a fully charged 60 ah battery would take over a week to go flat.
So either the drain is higher (or increases) or the battery is faulty/not fully charged.
Have the battery fully charged and tested, and that will only leave one thing which would need investigating further.

 

[Pedro86]

I hope for your sake it's not this as mine just cost £720 from Merc, at trade!

A word of warning though, its not good to jump these cars as that alone can kill SAM units etc!

£720 wow. Yeah a drain hasnt showed its face yet annoyingly!

Almost at a loose end.

 

[Pedro86]

.3 amp amp drain on a fully charged 60 ah battery would take over a week to go flat.
So either the drain is higher (or increases) or the battery is faulty/not fully charged.
Have the battery fully charged and tested, and that will only leave one thing which would need investigating further.

Yeah we are in the process of getting the new battery fully charged up.

Although i dont know how likely new batteries fail like this?

 

[Dec]

The alarm system is contained within the siren, there are batteries inside the siren, these batteries will get a constant power supply to keep them toped up when the car is locked or unlocked.

What I meant about the alarm working properly was does it sound off and do the hazards flash when it is triggered?
To test the alarm;

-Lock yourself inside the car.
-Stay completely still for 60 seconds
-Then open a door/ doors or bonnet
-The alarm should sound off for about 20 seconds and the hazards should flash for a further 2 or 3? minutes but without the siren screaming.
-The alarm should then reset itself… I think.
Unlocking the car or putting the key into the ignition will disable the alarm … if it goes off.

It’s a common fault… if the siren is the original factory fitted unit it is now 14 years old.

Just a suggestion, it could be anything draining it…if it is a drain.

Dec

 

[Pedro86]

Thanks for the tip. Anything is worth a try!

 

[jackmc123]

yes as referred to earlier ^^ about rear sam units. Control units that could be staying alive could not show on a discharge check until later on so do your discharge check as you would and rig it so you can leave it on the check and keep checking it you could very well have an intermitent battery discharge

 

[Terry_]

I would imagine its quite easy to find. 3-400 milliamperes is probably the alarm siren . It's about the right amount for this.
They will go flat in 3/4 days once the battery dies down a little

 

[Pedro86]

Is it worth me getting it hooked up to a diagnosis machine at the MB dealer? I'm guessing there not magic though!

 

[Pedro86]

I would imagine its quite easy to find. 3-400 milliamperes is probably the alarm siren . It's about the right amount for this.
They will go flat in 3/4 days once the battery dies down a little

The old and new battery where going dead in less then 24hrs.

 

[Terry_]

Well it cannot be a 3/400 milliamperes drain flattening a good battery overnight
The information is incorrect somewhere

 

[yorkshiregit]

Pull the fuse out & see if it doesn't drain you've isolated the system.

 

[Pedro86]

Solved!!

My passenger footwell was soaked due to the drain getting blocked with leafs and mud like substance. I lifted the footwell carpet and noticed a loose black cable almost like coax type which must have been draining to earth of the car.

Fixed the water leak and the battey now seems fine. I will have to up a photo of the loose cable.