do some searches on the power seat draining power. there's a cheap fix.

 

Thank you for your reply - much appreciated. I read some of those threads prior to my initial post, but they only seemed to be issues where the car would routinely die (without key fob and sunroof issues). Not sure if my key fob and sunroof issues make my situation unique or not.

 

I would buy myself an inexpensive clamp-on ammeter to check the current draw. Then try pulling fuse #8 (rear SAM, in the trunk) to see if it drops. If so, the problem may be in the ATA (alarm) module, located under the fender shroud, behind the front passenger tire. Try unplugging it, then replacing fuse #8 and check the current draw again.

 

Thank you so much. Did something I specifically said (key fob issue, sunroof issue, etc) lead you to believe fuse #8 is the issue, or is that just a more common solution generally speaking when a battery drains?

Appreciate it!

 

Fuse #8 feeds both the ATA module and the antenna amp (which responds to the SmartKey fob). The antenna amp often goes bad and then the remote control locking (RCL) function stops working, or only works intermittently.

A common voltage leak on the W203 is the power seat control, but that's usually only on the vehicles with the full 10-way power seat plus memory. Most C240s just have the part-power/part-manual seat with no memory and those generally don't have voltage leaks. But the ATA module is the next most common culprit.

 

I can't thank you enough for your very specific advice. My local repair shop is set to begin their investigate work tomorrow, and I will now call them before they open in the morning and leave them a voicemail instructing them to FIRST do exactly as you advise. I would just do it myself, but I am not savvy at all with this type of thing. If it is the ATA, is that a super expensive fix?

I DO have the part-power/part-manual seats, as you mentioned most C240s have. I'll have them check that as plan B if the ATA module isn't the solution, just to be sure (even though unlikely). Is there a plan C I should have them check if it's neither? Or am I just screwed at that point?

Again, I sincerely appreciate your help!

 

Update - the local repair shop pulled fuse #8 and a bunch of others, and still no luck. They were able to fix the key fob issue by disconnecting the battery. One thing they still haven't done is check the seat modules, but as rudeney mentioned, this isn't likely.

I feel completely lost now. Any other suggestions?

 

If it's a voltage leak, the best way to run it down is to put an ammeter on the positive battery lead, then start pulling fuses one at a time until you see a drop. It's just trial and errors. Another culprit can be the temperature sensor fan int he Overhead Control Panel - fuse #9 on the rear SAM.

 

Hi - is there anything else in the car that is not working? A random fact I found when playing with Canbus was that if the Canbus does not go to sleep the Can modules very quickly suck the battery out! Overnight will empty it. I put in a radio with the wrong Can version / voltages from an E class and it did this. A bit left field, but a can fault could do this.
Greg

 

FYI, the CAN bus itself is just wire - it's the devices on it that "wake up
or "go to sleep". There is no central controller for the BUS - it's basically a peer-to-peer network. There are, however, a few central connecting points for the bus. One is under the driver's door sill. If the car has been flooded with water, this connector can get wet and corrode.

 

i just bought a w203 1.8 2003 seat controls does not work, and always is the red code on the screen saying voltage failure, here in mexico someone did kind of jumper with the alternator. now car doesnt diischarge, but seats dont move electrically and red screen is always there. any ideas

 

Fix the voltage issues and then if that does not fix the seat problems, that will be a different set of diagnostic steps.