I run a 2002 C270 diesel and it has now covered approx 170K fairly trouble-free miles.
However, all was well until recently when, after just a two day break from being used and locked and in the garage, I found the battery had expired .This battery was only 18 months old and after a quick call to the supplier, a new battery was fitted and the old one was returned under warranty. Everything seemed ok for about a week, until the car was not used for a couple of days and the same happened again....battery flat and we had to jump-start the car. As you know these batteries are very substantial, so something is draining this at an alarming rate. With the ignition off and when connecting a jump battery, there is a tell-tale spark of a power-drain. No idea what could be causing this, as I have not had any new fitment added to the car. Anyone any ideas please?

 

Check to see if its the harness under your seat. Those have been know to drain batteries.

 

Many thanks for the reply.
Can this 'under the seat harness' be simply unplugged, without causing other problems?

 

It can I believe, there's a thread on it if you do a search

 

- Only use Genuine Mercedes-Benz car battery
- As per owner's manual, do NOT jump start car!
- Search in wiki for power seat drain

 

Sorry, I am a newbie here and I have just realised that this appears to be a common problem and there seems to be loads of info on here regarding a fix.
However, I would still like to say a big thank you to all the members who replied.

 

Seat modules not going to sleep is the most common cause of battery drain in the W203 followed by the HVAC sniffer fan in the overhead console.

 

No problem,... everyone of us was once a newbie too! And we all still have so much to learn.

All we ask, is that you post the solution that fix your issues,.... we have too many threads that only state problem and maybe possible fixes,... without the final solution. One day it'll help someone who's doing a search.

 

+ 1 .

Its slackness not to

 

Seems that I'm in the same spot as Jonathan at the moment! I've had a couple of dead battery incidents over the last few months after the car has sat for 7+ days. I'd say I can get at least 2-3 days holdup time and the car starts ok. A few questions for the learned....

1. With a decent battery and no unusual phantom current draw, how long should the car be able to sit around without use and still start up ok?
2. My car does not have power seats, but might it still have a seat module installed?
3. How can one tell if the temperature sniffer motor is the issue? Could you put your ear up to it and hear it running?
4. What is the normal maximum current draw for a C230 when switched off?

Thanks!

 

1. My car typically sits a week to 10 days,... and still fires up like a champ every time. My coupe is a "pleasure car",... I live on a subway line so most of my daily travel is via public transit,... sadly, I probably spend more time online on this forum than I do driving the car!!!

If you have problem with it holding a charge, it might be time to either get a new OEM Mercedes car battery or try a C-Tek trickle charger (OEM to the Mercedes trickle charger).

2. No power seat (very rare on coupe),.. no power seat module to worry about.

3. Turn off the car, take key out of ignition and pretend you're leaving (open door - close door) but stay inside,... wait,... and listen for little motor in overhead console,...

Also make sure all interior lights goes off (some even set overhead light to off so it won't light up with they open door),.... including those in glove compartment, centre console storage compartment - under radio/HVAC,... those little lights seem harmless, but they draw quite a bit of power,.... to test close the glove compartment or whatever with a small device recording video inside of it (most digital camera and cell phones today have a video mode),....

4. Not sure about our coupe,... but for typical cars about 50mA

 

I've had my car sit around for two to three weeks at a time; if you're losing power in that short of a timeframe, you've got at least one draw at work.

 

Here's an interesting link posted from Alswag, a fellow Canuck-le-head, on BenzWorld,.... a how to DIY on finding parasitic electrical draws
http://www.benzworld.org/forums/w203...y-morning.html

http://www.youtube.com/watch?feature...&v=KF1gijj03_0

 

A very informative video . Thank you SRT .

It should be put on a sticky ?

 

Great video, and other info! Many thanks!!

I checked the quiescent current draw today and things seem just fine. Generally did things the same as in the video and added an easy means of bypassing the meter for any time I needed to open a door.

My observations... Initially, current is around 1A when the battery is first connected to the car. After settling for a while it steadily drops, so the advice in the video to not pass judgement until 30 minutes have gone by is quite valid for our cars. At any given time the current does tend to regularly jump by about 10mA at a fixed period. After 30 minutes the current was centered around 30mA. After sitting even longer it dropped to jumping between 15-20mA. My meters are not exactly lab grade, so I double checked with a second one and they agree within 5mA.

So, I can pretty much conclude here that my battery is a gonner, even though the slow drain was characteristic of excessive parasitic current draw. The battery was new in April. Not a Benz oem, but it is a proper group 49 size made by Johnson Controls. Its at the shop now awaiting testing...

 

The Mercedes-Benz car battery list for $280.90 at Canadian Mercedes-Benz Stealerships. If you're near a border town or are thinking about cross border shopping,... the same Mercedes-Benz car battery will cost about $130-147 at American Mercedes-Benz dealerships.

100Ah 760 AEN (ColdCrankingAmps)
Mercedes-Benz Part#: 000-982-33-08 (Give them your VIN to double check part#)
$130-147 in USA $280.90 CAN in Canada

old: A004-541-45-01 Varta
Made in Germany
100Ah 760 AEN (ColdCrankingAmps)
Hoppecke

Dimension: 34.6cm (13 5/8") x 17.3cm (6 3/4") x 19.0cm (7 1/2") 50 pounds!

 

Have your battery properly load tested.

 

Just a quick update and I hope a conclusion to my flat battery situation.
Took heed of all the valuable advice given by members on this forum and began the investigation. Firstly, I charged the battery. Then sat inside car, closed door and thankfully heard the HVAC sniffer fan turn off within 45 secs or so. Next on to the underseat control units. Unplugged both drivers and passenger side and left car standing for 24 hours. Next morning, before attempting to start the car, I checked the battery voltage and this showed 12.6V which I believe is ok. Car started first turn. Replaced underseat plug on passenger side and everything has remained ok. Therefore the culprit is the underseat unit on the drivers side, which will be 'going under the knife' later today!
Just like to thank everyone on here for helping me to avoid depositing large amounts of cash into the Royal Bank Of Mercedes.
So a Happy and I hope prosperous New Year to you all!!!.....Thank you.

 

Suggest you replace with a unit from the W211.