RE: Electric problem

[georges 928S]

Hi Guys, need some help on my wifes car,Mercedes C240 2002 model. my question is what supplies power to the fuse boxes, is it relays or some thing else. i was checking my fuses with circuit tester using my power supply unit for power and i think i blew some thing and know the cluster shows 2 faults one reads TELE AID and second one says RESTRAINT SYSTEM VISIT SHOP can any of you help please. Ed. 928 owner.

[tisilrad]

You should always use a logic probe when checking circuits on newer cars. Is the fuse block completely without power? Do you have an OBD2 scanner to pull codes(though i doubt these specific codes will show up...they are not drivetrain related.)? Do a google search on the specific outputs and you will be able to retrace where the problems are derived maybe ..sounds like you have shorted one or more of the control modules? You will probably need some kind of wiring diagram for any serious work here. sorry .

[georges 928S]

Hi Tisilrad, thank you for answering me, i have power to the fuse boxes and i also used my obd2 and gave code P0600 and also says (serial communication link pending) what aver that means. back to you. Thanks Ed.

[tisilrad]

CAN_BUS communication error possibly. I have a feeling you have a control module shorted or possible problem in the PCM? I would have to do some research on that.
I would try disconnecting the battery(make sure your key is in the off position) for about 30 min. to reset the system but i cannot guarantee that wil work for your particular problem...I assume it is not running right now? hate to tell you but it will probably require a dealer reset or reprogram to fix..at the least. Control module replacement at the worst.

[tisilrad]

After some research...check your battery voltage, charge or replace...i am guessing it is the orig. battery? make sure you replace with a battery of equal or greater cca...factory components are always recommended for Mercs due to the sensitivity of the control systems to variants.

[georges 928S]

Hi Tisilrad, what does can-bus and pcm stand for in words, and my battery is new 2 months old and the car starts fine just like before i touched it. this all happened when i was checking the fuses because my partial drivers power seat and back window shade did not operate. back to you. Ed.

[tisilrad]

the can bus is the communication system between the assorted control modules..to put it in basic terms, and the PCM is the powertrain control module...or ecm (engine control module).newer cars like this have 50 or more assorted control modules and the code output seems to indicate a lack of communication. not sure where of course , the dealership scanners may be able to pinpoint the problem where a standard OBD2 cannot. did you try disconnecting the battery..from what i have seen those p0600 codes are intermittent...it may come back eve if it resets..generally requires 30 min or so of driving. I would guess that the control module for the nonworking systems(seats?)is what the problem is...the primary processor is not receiving a signal from that particular module...check and make sure all plugs into electrical modules and relays are tight, only after disconnecting the battery should you do this to risk a short and to prevent random static discharge,.you should make sure you are grounded before unplugging any as well(with an proper grounding strap around your wrist) . This will take some time and partial disassembly of the car of course so if you start along this path expect to put some time in it. I dont envy you in this.

[tisilrad]

Also BTW, remember to check all your fuses and associated relays before embarking on such major repairs, though i doubt this is your problem, but maybe you will be lucky.

[georges 928S]

Hi tisilrad, thank you very much for your help,i will try the fuses and relays and undo the battery first if that dont help i will take it to dealer. i will let know what happens. Thanks again. Ed.

[Alan in AZ]

I don't understand how you were testing exactly but never do that again it is very BAD idea to connect any additional power to your car that way - buy a cheap DMM and use that.

Most fuse boxes are fed variously by direct battery supplies (probably your problem) and some switched supplies (often just from the ignition switch, sometime via relays or other electronic controls) these are usually ignition, accessory, radio, sustained power etc rails.

If you don't know whats what - just test fuses out of the car using the DMM on ohms mode.

If you know whats what you can probe ATO/ATC fuses while in situ - see the little unmolded indentations above the pins - use the DMM in voltage mode, with pointed probes...

But mainly if you don't know what to do - ask first..

Alan