W220 S320 huge battery drain-help

[Paulkelly]

bought car with battery drain,however worse than advised. Loses 2 volts overnight. Ammeter suggested 8 amps drain,disconnected fuse for sat nav,drain now 5.5 amps. Obviously no internal lights on. What could be still on that uses that sort of amperage? Any and all advice appreciated.
cheers
paul

 

[Blobcat]

Hello and welcome,

Comand system is a good candidate

 

[John77]

I had this with my wife's SLK. It would actually go flat overnight and after pulling each fuse one at a time, I found that it was the Towaway system that was draining the battery. Left the fuse out for that system and no problem since. The only irritation was that it was the last fuse box in the boot on the rear SAM where that fuse was lol. Boot or Bonnet light? That is the thing about electrics. It can be anything. Don't rule anything out because you are told it can't be that. That is what I was told, but it solved it.

 

[ajlsl600]

Some while ago I bought a nifty bit of kit that goes into blade fuse fitting and gives a readout of what the circuit is drawing. Some systems that supposed to go sleep when you close up car, don't go to sleep..
Are u locking car in evenings

 

[Paulkelly]

Thanks for responses.
1 pulled fuse for command as inte4net suggests common problemm. dropped drain from 8.7 to 5.5.
2 it is not an internal light
3 only had this car a week,have not locked each night
4 today with a friend we pulled every fuse ,did not make a differ3nce. Left ammeter attached had a brew-ammeter suddenly read 0.5-happy days.
5 car home,drain now 1.87 amps. Pulled every fuse-no difference.
so as I write this,battery disconnected-on smart charger. Tomorrow is another day.
happy to take all advice offered-thank you

 

[Craiglxviii]

Starter motor ground or diode pack in the alternator, would be my guesses. The diode pack is a particular weakness in the 220 platform.

 

[Paulkelly]

if it is diode pack-not sure how to check.
simply replace alternator??
tks again

 

[Craiglxviii]

if it is diode pack-not sure how to check.
simply replace alternator??
tks again

The diode pack used to be available separately, but when mine went in 2019 I ended up going for a new alternator.

 

[Paulkelly]

So £120 for a new alternator is not breaking the bank. But how do I know if that is the issue?
cheers

 

[Blobcat]

So £120 for a new alternator is not breaking the bank. But how do I know if that is the issue?
cheers

Get it off and take it to an auto electrician or pre some old boy who’s been refurbing alternators his whole life. They’ll test it for you and repair it for much less than a new one.

 

[ajlsl600]

The diode pack used to be available separately, but when mine went in 2019 I ended up going for a new alternator.

When my 208 alt shxt itself changing req easy diode pack not so much...

 

[malcolm E53 AMG]

This is worth investigating:

Intermittent battery drain W220

I can see battery drain is a common problem. My S400 CDI is in daily use and on four separate occasions over the last yearI have found the car dead. usually overnight, but one incident actually happened after work… Seems to be somethnig happening randomly, but the powerdrain must be significant...

forums.mercedesclub.org.uk

A regulator diode failure was a red herring in this case make sure you read the last post

 

[Craiglxviii]

This is worth investigating:

Intermittent battery drain W220

I can see battery drain is a common problem. My S400 CDI is in daily use and on four separate occasions over the last yearI have found the car dead. usually overnight, but one incident actually happened after work… Seems to be somethnig happening randomly, but the powerdrain must be significant...

forums.mercedesclub.org.uk

A regulator diode failure was a red herring in this case make sure you read the last post

This is very true. Hunting the drain using the fuse box is necessary.

 

[SL63 Mark]

5 amps is a hell of a drain. I went through my fuse boxes on my 230 with a current tester, they are about £10 on eBay and could save you guessing. Or, just use a multimeter in series with the battery set to Amps, and pull the fuses one by one. In the end it was my rear window motor pulling half an amp. They fill with water on the 230.

5 amps sounds like your headlights and heated seats are on. Have you noticed a warm bottom ?

 

[mioba]

there is a fuse box in rear passengers area too are you aware.

for the W220. An invaluable resource is

W220 S-Class Encyclopedia

w220.wiki