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2001 c240 problems

5K views 14 replies 3 participants last post by  johnhef 
#1 ·
Hi all,
This is my first post on this forum as well as my first mercedes. I bought a 2001 c240 at an auction a couple months ago. When I got the car to my house(first time I actually saw it in person) I noticed the radio had been ripped out and the plug to the stereo harness was cut. I thought it would be no big deal since I wanted to put in an in dash DVD head unit anyway. I installed the head unit and it worked for a couple days.

One sunday I went out to move the car and noticed the alarm was going off faintly. The remote on my key wouldnt work so I had to use the trunk key and crawl through and unlock the door manually. Ever since then the battery will stay charged for about a day. Ill leave the trickle charger on it if I need to move it around my shop so it will start. When it does start my headlights do not work, and my brake lights do not work. I thought I might have blown some fuses during the install, but I noticed when I used the remote to lock it the other night.

I also have a OBD2 scanner I was trying to hook up so i could read the 3 fault codes, but the scanner will just say connecting and never actually connect.

My first thought was that the ECM might be going or is bad. Any thoughts on my list of problems? Any input would be much appreciated!
 
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#2 ·
With the ATA (anti-theft alarm) siren sounding and the RCL (remote central locking) not working, I suspect fuse #8 (rear SAM panel, in the trunk) is blown. The ATA siren has its own backup battery and it will eventual fail, leaking "acid" all over it circuitry, which will blow fuse #8 (its feeds both the siren and the antenna amp, which controls RCL). The solution is to replace the siren, but in the interim, you can unplug it and then replace the fuse to restore RCL functions. The siren is located under the fender shroud, behind the front passenger wheel.

The battery drain could be many things. Do you have the full power seat option with memory? If so, that could be it. There is a fix for this on the forum that rewires the seat controller to only work with the ignition on.

if you are going to do your own work, I suggest investing in a decent scan tool. SDS is "the best" but it's complicated and will cost $300-$500. iCarsfot i980 is plug and play and costs about $120.
 
#3 ·
Thank you for the quick response! I am going to head out to the garage to look at the fuse and the alarm.

As for the battery, my seats are manual sliding and electric for the rest, no memory. The scanner I have is ScanGauge2, borrowed it from my brother. My electronic car tools are limited to mustang tuners, trying to branch out a bit with this benz.
 
#4 ·
I checked the #8 fuse, it looked good, but removed it to be on the safe side. Going to unplug the siren and replace the fuse tomorrow. I was looking at the fuse diagram and it looks like #62 relates to the OBD2 port, headlights and brake lights, which might explain some of my issues. I replaced the fuse on that circuit and still have the same problems. Would any of the stereo wiring also be on the #62 circuit? I am suspicious of the stereo since the molex plug was cut off. I was thinking of trying to find a new one and solder it on and then use a reverse harness to finish out the head unit install. Any ideas on where to find one?
 
#8 ·
Im finally getting back to working on this c240. My battery/alternator light is on, if my alternator is bad could that cause electrical issues such as the brake and head lights not working? I would assume that if the alternator is bad this could be what is draining the battery. Any thoughts would be much appreciated!
 
#10 ·
I was getting the tele aid malfunction light, so i removed the two fuses associated with that and my parasitic amperage draw went down a bit. I still have a draw on circuit 52, I am reading .8 amps. Is that an acceptable amperage draw? The only thing I am seeing on that circuit is start enable. I am starting to think that my ecm may be bad since now my electric fan kicks on after shutting off the car. This car seems to be a headache.
 
#14 ·
I had the battery and alternator tested twice, both were tested fine. Is there a way to test/reset the ECM? I believe this is the cause of the problems I am having. The fan running at high seems to at least be related to the ECM. I have seen this procedure for other models but wanted to find one specific for the c240 of this year.
 
#15 ·
hi, any faults in the engine control unit now? what are actual values of the coolant temp sensor if you can communicate with the engine module? typically fan running full tilt is indicative of an issue where the ecu cant see what temp the sensor is reading or no communication with the engine module at all. there's probably other situations as well but thats what first comes to mind.
 
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