Battery Charging and Electrical Problems
 

W203 C200 2001 19kmiles

I need to jump start my car everyday because the "electricity" gone.Battery & alternator tested fine.My mechanic still cant solve the problem yet.Can anybody help me?Thank you

How were the battery and alternator tested? Were they tested in the car using an instrument that just touches the positive and negative terminals? The kind that AutoZone will do for free? In my experience, these are not thorough tests of these components.

The alternator should be removed and placed on a testing machine which will spin it up to speed and measure not only volts, but more importantly amperage output. Similarly, a dedicated battery load tester will provide a more accurate test of your battery by simulating a deep discharge. I believe Autozone may perform these tests, but I'm not sure. Old-school type parts places which *tend* to have more knowledge will definitely do these. Napa and some local CarQuest places come to mind, depending on where you're located.

In my opinion, the in-the-car tests are just for rough overview but aren't very thorough. It's similar to the handheld code scanners which just give you a rough guide to start troubleshooting but don't really tell the whole picture.

If it has the original batttery in it, I would replace that as a first step. Five years in a car that sits a lot is about all you can expect.

Len

I generally agree with your observation, but a load test could still rule out the battery. Why replace something that is perfectly fine? $$$

Only because he is having electrical problems, the battery is approaching or has passed its useful life and not running a car much is hard on a battery. Batteries now often fail without warning even with passing a load test. Now if the electrical system was functioning properly, I wouldn't automatically swap it out after five years, but it certainly would be on my watch list. Of course, we aren't sure whether or not this is the original battery or not.

Len

I replaced the battery with the new one about 2 months ago.Not the original merce battery but with bosch battery.And about the alternator,my mechanic use his "computer tools" to test it.Thanks.

Okay, so the original battery question is answered. :)

Len

Uhmmm...parasitic drain too high?

I presume the new battery has the correct CCA for your car and the electrolyte level is fine. Check that the battery connectors are clean and tight.

Must I use a special tool to clean it?

The W203 chassis has an interior network of computers... if the network doesn't go to sleep with the key off then there will be a constant drain that will kill the battery..

.Does your car have power seats with memory?

Use a battery wire brush ... male brush for the connectors and female brush for the terminals. Should be available at any auto parts store or Sears.

Yes,it has.Are there any off button to shutdown it?

One of the first steps would be to check "quiescent current", MB word for the drain on a battery with everything off. I had a 89 SL that had a frayed wire bleeding from the trunk lamp circuit to the running lamps, and would not do it when the lid was up and they had a meter on the battery

I have wondered about this before. How exactly does one take this measurement other than hooking up a milliammeter inline?

hook an ammeter inline with the negative cable and let the car sit and check your draw after sitting 30 minutes. 203 should be about 50mA or less.

Thanks Ferdman.I tried it but still dont work.Today,my mechanic told me the car is using 0.8A (0.5A for normal car) without the engine starts.Something is draining the battery.

That is way way to much amperage draw. A 2001+ C class should draw
between 20 and 50 milliamps with the car locked after 45 minutes.
your car is drawing 800 ma. Front power seats, GPS Comand units, Phone
PSE control units and Rear Sam control modules are all common draw issues
on that car. You will need to isolate the circut with the draw.
The Prefuse box next to the battery is a good place. You can remove power
from all the main power sam/fuseboxes on the car whilst watching the draw
one at a time.
Once you disconnect the fuse box with the draw, start chasing circuts one by
one by pulling fuses and disconnecing ecus.

Good luck and remember, it takes some ecus over an hour to got to sleep and stop drawing current. (E-call and GPS)

Euro cars with stationary heaters can have draws from the heater controller
as well.

Regards,
DR.D