Seadoorxpguy

Well after reading through A ton of posts and spending the majority of my Sunday to diag the issue I'm at a loss. I started at the seat modules. Still drains. Checked for voltage drop across all my fuses. Nothing out of the ordinarily. Pulled the fuse for the telecom system. The battery in the car is brand new. Alternator charges at 14.1. Shortly after the car is off the battery is already down into the low 11s. After 24 hours it must be jumped. I'm typically very good with auto electronics. I build ls1 swap harnesses and work as a technician. But this car is kicking my butt. It's my dad's car so I'd like to get it fixed ASAP

samaritrey

did you check the upper console fan? Have you load tested the battery? Also did you get the correct battery for the car almost all of the ones that can be found at auto parts stores are not strong enough.

funnyent

Do you have the bose sound system? My C230 was dying and I checking everything common, but couldn't find it. Took the dealer 2 days, but it was the amp for the bose sound system killing the battery. Dealer wanted $1800 to fix, so I took it out and put in a cheaper aftermarket system and it's been fine every since.

Seadoorxpguy

The aircon sampling fan? Checked it. It's in front of the shifter on this model. Shuts off as soon as the key is off. The battery is brand new. Haven't load tested the battery but voltage drop on cranking is very minimal. The battery is the correct size also. No Bose either. Aftermarket head unit. Checked all 3 fuse centers for a draw. Couldn't find anything. The more I read I found there were some people with voltage regulator issues. Possible bad diode causing a draw. Best way to diag?

Seadoorxpguy

Anyone?

mleskovar

Best = Star Diag but even that doesn't necessarily find all, especially electrical problems. Sounds like you have a short to ground. To check if the alternator diodes are the problem disconnect the alt and see if it still drains. Resistance checks on the diodes is another if you can get to the right wires and isolate them. An amp meter clamp around a battery cable would help troubleshoot.

Carsy

As mleskovar says an amp metre across your battery & pull each fuse in turn.

corkshoppe

i had that happen in my s class, after a year of battery tender, i took to dealer and they replaced the front sam unit, never had problem since.

MJ50

do u have any mods to the car as far as electronics?

samaritrey

Your car should actually have two just like the other w203's one in the climate control and the other next to the sunroof controls which has been known to go bad.
https://mbworld.org/forums/c-class-w...nnect-fan.html

Seadoorxpguy

The car does have a aftermarket head unit. Checking for voltage drop across the fuses is basically the same as yanking them out and looking for a drop with a meter. I took the sunroof control panel apart and there wasn't one in there that I saw. I'm going to try to disconnect the alternator this weekend. Any tricks to this. Sense it's my father car and I have to go to his place to work on it. What should I bring?

mleskovar

You are looking for a current drop, not a voltage drop. Clamp on sensor at the battery is the best way. Normal current is about 35 ma. with everything off. You have to wait like 5 minutes for the buss to go to sleep before making the measurement. Every time you wake up the buss....like opening a door, turning on a light, inserting the key etc. you have to wait again.

krazzdav

Seadoorxpguy,
If you don't have an amp clamp you can just use a multimeter. If you don't have that you can use a test light. The test light will be more of a guess by how bright it is. With a test light it should be very dim but in both instances you disconnect your negative battery cable and connect the leads of your tester in between.

Here is a video explaining what you want to do-