C220 CDI Coupe Battery Draining Problem

[Russ Clarke]

Hi Guys, I am new to the forum & the world of MB (well apart from an A Class my wife had a few years ago but we won't go there!) and need your knowledge already!

At the weekend I bought a 2002 C220 CDI Coupe auto with 82k on the clock and full dealer service history - nice car and being as I will be putting around 30k on a year I was after something nice but not too expensive and something that should be reliable, well I have to say today disappointed me.

I used it at the weekend without any bother and went out to a rather frosty morning today at about 6am and zero degrees. The car burst into life at the first turn of the key and I was on my way to my weekly visit to my office some 120 miles / 2 1/2 hour drive away. I arrived around 9.00 am and locked the car via the key fob & went into work. came out at 12.30 for lunch & couldn't open the doors due to the battery being so flat! I entered the car using the emergency key and all electrics were well dead. Tried jump starting off a friends Tiguan but nothing. I called the AA rescue guy who got it turned over after using his booster pack.

He ran all the usual tests and concluded the battery was holding charge & the alternator was working correctly but as soon as everything is switched off the battery is being drained by around 25 amps - easily enough to completey drain it in 2 hours.

I don't have electric seats or anything like that but the AA man thinks it maybe the engine block heater as that is allegedly a common fault on this unit? Trouble is he couldn't locate it to remove & see if it is the culprit.

Basically he couldn't help me further and left the car running telling me to get it booked into my garage for further investigation.

Can anyone help further - is this a common problem because if so I don't think I will be keeping my Mercedes and will go back to my Saab!

Any help is greatfully accepted as you can imagine I am slightly fed up with having the car for two days then being let down like this!

 

[doubledecker]

earth

hi russ,check out the earthing from the battery to the body is clean and tight on,a good trick is get a start cable put it on your minus (blue pole) and connect to a shiny clean bit of steel,then check your charging,on the 124 model the earth strap is attached under on the right side of the gearbox to the wishbone right back

 

[jefrs]

Just an idea - check the volts on the many fuses to see which ones are live when it is switched off. Some should be on but there's at least one that should not.

 

[Alex Crow]

The AA man is on the money, this time, it is mounted on the engine block above the starter.

Not an especially common problem, but a known one none the less.

 

[AMG19]

Russ this is not uncommon problem and could be the source of the drain. However I would start with doing a drainage test and locating the definate source, pulling out fuses and relays checking drainage. There are lots of possible things that could cause your substantial drain the heater is just one.

 

[Russ Clarke]

Thanks for your help so far guys. The car is now with my local independent Mercedes garage who tells me the issue is with the alternator? He says he can't find a drain on the battery but the alternator isn't charging the battery correctly? He says although it is giving out voltage (too much he believes) there is not the correct amperes or whatever (forgive my ignorance, I am definitely not clued up on car electrics!). When I questioned if this would drain the battery after it was fully charged, he mentioned there is a possibility of a short in the alternator itself which could drain a charged battery but until a correctly functioning alternator is on the car, he is unable to proceed with further diagnostics.

My concern is that he will fit a new alternator (quoting me around £600 + VAT) and it won't cure the problem. As I say I really don't understand car electrics but I don't believe a faulty alternator is at fault. However, IF he has diagnosed correctly and there is no drain currently on the car, that surely shows an intermittent fault that will be very hard to diagnose?

 

[jaymanek]

I would take it elsewhere.

 

[Alex Crow]

I would take it elsewhere.

My thoughts too, if the guy says the alternator is supplying plenty of voltage, but not enough amperage, he is does not know enough to repair you car - to put it subtly.

 

[ssrs]

Hi I had exactly the same problem, the battery drained after about 1-2 hours after working perfectly . the weather was cold also. I had an auto electrician look today, he spoke to a mercedes tech on the phone and the first thing he told him to do was check the heating element in the block. He found a high current draw with the ignition off (27A) from the engine block heating element which is mounted just above the starter motor , well hidden from view. He removed the connection and isolated. we agreed that the climate is not cold enough for this to be required and left it isolated
Hope this is of help to anybody in the future...

 

[panason1c]

As mentioned, i very much doubt that the alternator is at fault in this case, i first would locate the fuse for the block heater and remove it to see if that stops the battery drain.

 

[142 TPL]

I'm interested to know if this heater booster drain fault starts as an intermittent fault

 

[grahamdias]

heating element by cooler

i have a similar problem, car is losing all charge in battery when parked , i put the amp clamp on the battery with no key in ignition and is losing a lot of power when car off, took it to mercedes they think that its the heating element in the engine and is short fusing thats why the power is going so quickly , quoted £870 including labour , not paying it so looking for way to resolve