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Old 08-20-2004, 04:16 PM
I can fix it, I just need
Join Date: Aug 2004
Posts: 14
DTC codes? Insane Air Conditioner...

I have a 1995 S500.

Will the cheap Radio Shack code reader work with this car? Or does it require a full digital reader?
To shortcut some details about code readers, here is my problem.

I started receiving a CHECK ENGINE light last year. The car ran perfectly, except for one day when it had a bad miss for about twenty minutes. It then went away. At a service, I had the dealer check it and they told me I had a bad wiring harness to the engine control computer and also corroded distributor caps and rotors. They said it was a $2100 fix. I told them to shove it. I cleaned my rotors and caps (they were funky apparently from water intrusion during an overzealous detail or something). The car continued to run well and the weird miss never recurred. The CHECK ENGINE light just became "normal" as far as I was concerned. Also during this time, I had to run the car thru emissions testing for new plates and it was squeaky clean as always.

Last week, I stopped at a neighbor's house and spoke with him in the driveway (me in the car, him standing outside). His toddler child was acting up and needed attention so I tossed her my keys to play with. She proceeded to lock and unlock the doors thirty of forty times. When I went to leave, I retrieved the keys through my open window and went to start the car. Since the doors were locked (from outside) the alarm went off. I pulled the keys out and shut off the alarm, started the car, and drove away.

As I drove away, I noticed my dash vents blowing hot air. Also the defroster was blowing hot air. Not just uncooled, air, but hot air. The AC display was reading normally and showed 70 degrees on both sides. I went to change the temp and nothing responded (the display had normal lights and readings in the LCDs but nothing would respond). I went to change the blower speed and nothing responded. I went to pushing buttons and nothing responded. I rolled the windows down so I wouldn't melt.

About this time (it was dusk) I turned on the headlamps. The AC display went blank except for the EC light. I turned the lights off, the display came back on but remained unresponsive. I pulled over and shut off the car. I restarted with no change (same frozen display). When I got home I disconnected the battery and left it off for four days.

When I reconnected the battery, the car started normally (a bit rough at first), the AC display was normal, and the air worked normally. The CHECK ENGINE light was out, and the day went well. The next morning, I started the car and the air went on full hot and the display was frozen and the CHECK ENGINE light was on.

The car is currently sitting with the battery disconnected again and I plan to retry tomorrow.

Any ideas?
Can I use the cheapo code reader on this car or is it a digital system that is not compatible with the cheapo reader? Can I use the LED and pushbutton on the N59 box? What do those codes mean?

Any ideas about the possessed AC?

I'm a newbie and hope I have presented my inquiry properly..


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Old 08-22-2004, 12:04 AM
I can fix it, I just need
Join Date: Aug 2004
Posts: 14
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Old 08-22-2004, 12:16 AM
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Old 08-22-2004, 01:13 AM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Arthurs link might help if the display responds. I doubt a code reader will help much. If you have the wiring harness problems, they will have to be fixed. Its best to do it before taking out a control unit or two.
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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Old 08-24-2004, 08:49 AM
I can fix it, I just need
Join Date: Aug 2004
Posts: 14
The A/C Diag link presented is handy, but I am getting complete blank-out of my AC display. It either works perfectly, or it becomes completely unresponsive or even blanks out. When this happens, it blows at about 80% blower and pours heat out everywhere.

When it does this, I DO get a check engine light, so I figure a code reader would tell me what's up.

BIG QUESTION: Tell me about the wiring harness issue. The dealer alluded to this earlier but I thought it was BS. Tell me what wiring harness we are talking about, why it fails, where is the best place to get a replacement, how tedious the replacement job is, and whether it is okay to just solder on a new harness end connector...

Is it possible/probable that a harness issue is causing my AC issues?

Thanks for any help.

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Old 08-24-2004, 09:32 AM
pcmaher's Avatar
Big Black V12
Join Date: Apr 2003
Location: Chicago, IL
Posts: 430
Check out Jim F's webpage mcollinstn. He has a S500 coupe, and has created a very comprehensive webpage. I attached a link to one of his pages where he sells a listing of codes, and what they mean. There is also a link to info on how to build an inexpensive code reader.

Code reader link...

I built one of these and ordered his manual. I was able to pull a lot of codes with this setup, but not all codes. It works for all non-digital circuits. There are some digital circuits (the SRS system is one of them) where this code reader will not work. But it may work for the Check Engine systems. He could verify this.

The wiring harness issue is a problem with many Benzes. This is the story in a nut shell, learned from reading the numerous posts on this and other forums. MB wants us to believe that they are environmentally oriented, and developed a wire insulation that breaks down more easily for recycling / land-fill reasons. Unfortunately, it worked too well, and can start to degrade in the car. High under-hood temps seem to accelerate the problem. The insulation actually starts cracking and flaking off, which is a bad thing when wires run parallel to each other. MB owners have been getting all sorts of goofy problems, and many of them are traced back to this insulation issue. I don't know if this is what's causing your AC problem. The injector harness is also affected by this. Once the wires touch in this harness, you can get injector misfires that will really cause problems. I have a V12, so I'm not sure where your injector harness is. Mine runs right down the middle of the intake manifolds. Pop the cover off, and take a look at the wires. Twist and bend them to see if the insulation is intact. I've read that some people saw completely bare and corroded wires once they started looking. The harness can be purchased, and you can install it yourself if you're handy. I've even read of an owner who simply replaced each wire one at a time to make his own harness, and with success! Do a search on this subject, and you will find lots of info.
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Old 08-28-2004, 01:03 PM
I can fix it, I just need
Join Date: Aug 2004
Posts: 14
Thanks, that's the first time I have had the wiring harness issue explained to me. Up till now the dealer has simply old me that there may be a wiring harness problem, and that resoldering a new end will not fix it. The insulation issue makes sense. Unfortunate, but does make sense.

Yes, I had already been all over the website you mention. I was under the impression, though, that my ECM output digital codes (and he emailed me to also say this) and the cheapie wouldn't work on my car. It's sure cheap enough for me to give it a shot though.

Thanks, and sometime next week I'll play with the car to see if I can make some headway.

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