I was wondering if anyone had schematics for the ECM CCM and the connections between them for a 92 LT1 car? I have some troubleshooting that I need to do but I need a good understanding of the components and how they interact.

I bought a service manual on CD but it is not the factory manual and the wiring diagrams are corrupted on top of that. (be careful of what you buy on Ebay) I won't be able to get a real factory service manual for a little while (althought I need one real bad) so any help I can get here will be appreciated.

 

there is one line... the Serial Data Line. I will have to check my 92 manual to get you info on it.

 

My friend, I have been on a quest for some time now to find CCM, ECM and PCM schematics. I have found some for other cars but not for our types of cars. I'd give my spare tire up for that information!

If your are really getting down to that level of electronics and repair, I think you know you really need the offical GM red book by Helms. I think you know that, and, you will love the information on the electrical as am an electrical type and appricate the real deal on info.

If Bogus gets you the info on the serial line thats great. Don't have my books here. Just wondering, what is your original problem you are having? Charge on

 

The current problems.........let's see

1. SYS indication
2. No fuel mileage data (0 mpg at a stop and 99 mpg going down the road)
3. Some of the codes I have:
quad driver 3 fail (I think it is 3)
data communications error
key error (source od security light I think)
4. Solid SECURITY light when car is running
5. No engine data on digital display but analog gauges work fine

There may be other problems that I am not remembering right now, I will have to run another diagnostic tonight and update this list. Overall the car runs good but I want to fix these things. I believe they are related to a single component failure and would like to track it down. I do need the diagrams though. I am an electronics engineer and I have every intention of replacing the quad driver in my ECM but before I do I want to know what it drives so I can check those systems too. There has to be something wrong that ties this all together.

I will appreciate any help you may have and I will share what I find with you. I will get an understanding of this system one way or another.

 

Sounds like we run in the same circle with the electronics. From memory, what I remember the sys indication is driven by the CCM. Most of your problems are linked to CCM functions. The ECM mainly runs the engine and powertrain and CCM the rest like security functions and car stuff. I believe you have OBD1 and so do I. How did you obtain your error codes. I think they come from the CCM, if its not performing correctly, possibly the data is flawed. Just suggesting. Make sure the battery is in good shape and the charging system (alternator) is operating correctly. Not saying this is the trouble but this has to be right on these cars on order to move forward with troubleshooting. Not much more to offer right now offhand but will look at my books tonight and see if I get some good thoughts. Happy hunting.

 

I agree, it does sound like a dead CCM. The SYS message is from the CCM... and the C41 is surely a problem with the CCM.

Any errors with the ABS/ASR? If so, that's it... you have a CCM problem.

 

I got my codes from the CCM right on the dask board (the paper clip trick) and used a code matrix that I got from the C4 guru. They are consistant. I did recently replace the battery. It was bad when I bought the car. I also found a bad short in the power seat circuit and repaired it. Figured this was the cause of the battery failure. The car still seems to have a draw though. I do not notice a problem with everyday use but upon returning from a 2 week trip my battery was completely dead. I plan to sort that out soon. I have a good 14+ vdc from the alternator (that instrument is working digitally).


I think the ASR is not working. When it is on I can still burn the hell out of my tires. I am not getting error codes associated with it though.

Are there common component failures in the CCM? I would rather try to repair it right now as opposed to replacing it.

 

you will not be able to repair the CCM... unless you can find a bad cap or resister on the board... if an IC is bad, I think you are screwed.

 

My ongoing CCM saga:

http://forums.corvetteforum.com/show....php?t=1218103

 

This past week I decided to measure the battery drain (everything off) so I would know what it should be if something did happen. I had to measure it on the 10 amp range. I could not measure on the lower range because not enough current would pass thru the ammeter to engage the CCM and bring the systems up. Have read about this in Forum so I understood what was going on. Bottom line is that I could not get the resolution on the ammeter I wanted and had to make the measurement on the 10 amp scale. The meter would bounce between .020 and .030 . Since it favored .030 it probably is in the upper 20 milliamp range. I used a Fluke digital to make the measurement. The hood lights came on when I opened the hood with about 4 amps.

As far as CCM failures, I have no personal first hand experience at that however what I have read on the Forum is that plenty of people have replaced the CCM and it never solved their problem. I guess they go bad but I’m really thin on that info. I have never read that anybody been inside of one or fixed one.

By the way, I have been in some of the boxes to fix. The circuitry like IC chips and such are proprietary meaning you cant cross the chip or find out its function using data sheets because they have marked it with a GM junk part number and not a IC manufacture regular normal part number. And finding schematics has been next to impossible, they want it all locked up to protect their stuff from guys like us.

OK – I’m back, feel better

 

I have read over all the posts again and according to the books, it looks like everything that was said is correct. The CCM drives the whole dash/LCD display. The serial link does connect PCM to CCM and links to ASR and A/C programmer. It also comes out at the ALDL connector I beleive at pin M for the 12 pin ALDL connector. I think it is a 8192 baud rate and I have look at my serial data about 8 months ago with a scope. Dont remember what it looked like but is was a slow signal, at least you can tell if anything is there. I have no idea what the action is between the CCM and PCM/ECM or what the prodocall is. If I get to look at it again I will post it but it could have been about 5 volts - as a guess for now.

Pins E13 & F12 on CCM tied together and go to D29 & D30 on PCM tied together (all 4 connect) and down to M on ALCL for serial data. This info from my 94 book and beleive you have the 12 pin on your 92.

Sure sounds like the CCM is classically bad though. I would disconnect battery and clean contacts/pins on the PCM and CCM. I would think it would be best to use an non oil base cleaner and pastic safe. use canned air and dry completely - real important. If you decide to go inside the CCM, look for and bad solder at the edge connectors. Check serial line for short.

My opinion is ECM probably OK since engine is running good and it is driveable. Hope this give you some ideas. At some point you will have to throw a part at it.

If some one thinks I made an error somewhere, jump in and correct it. Charge on

 

give me a few days. cant drag and drop or right click and copy the pages you are looking for from the program i have. need ink for the printer. i can print the diagrams for your year model. ill print and scan and post them. pm me if you still want them.

 

If you are using MS Windows you can hit CTRL+PrtScn to copy the current screen contents to the clipboard. Then you could paste inside an image editor and saves as a JPEG to upload. This assumes you can scale the document you have to fill the entire screen. Just a thought.

 

tried the ctrl+prtscrn nothing happened.

 

I found that after my last post yesterday. There is a lot of good info there.

I agree, I just need to track it down and make sure it is not a wiring issue. I am hoping I can fix it easily.

Code Update:
These codes are from the CCM in the dash display

1.1
C41
H53
H74

4.1
28

9.1
H62
H72

 

Another interesting thing......yesterday afternoon when I left work my ASR was working (it was raining out) however part way home it was not working anymore. There were no warning lights associated with the failure.

 

Every now and then my ASR will quit but it always throws a code and the SES light comes on. I think its from a faulty TPS sensor tho.

 

There are 2 ways to do this.

1) Use Alt+PrtScrn. Open up your program with the manual pages and then press Alt+PrtScrn. Then open an image editor like MS Paint or something much better and FREE like IrfanView. http://www.irfanview.com
Select PASTE from the clipboard. It will paste an image that is a complete image copy of the active program window into the editor which you can save as a jpeg or tiff file. Use the least amount of compression possible for the best image result. You can post the saved image or email it like any other picture.

2) Use Ctrl+PrtScrn. It will paste an image that is a copy of your entire desktop screen into the editor which you can save as a jpeg or tiff file.

 

Q-cat - A little more info. I measured my serial data line tonight with a scope and it looks like a bunch of square waves, superimposed on each other, bunched together and kinda jumping around. You can sync it up but not solid. It was 4 v p-p and set the scope at 0.5 ms/division. In rough numbers it looked like about a 2K rate but hard to tell where the rising and falling edges are. With door closed and key out it goes to sleep mode about 10 seconds or so. Turn key on and the waveform appears and stays (almost anything will wake it up). I just turned the key on (no engie run). This at least might give you something to shoot for. Good luck.

P.S. - This computer configuration is called a master slave setup which prevents data collisions on the bus. I would assume the CCM is the master. In the active mode there is always chit/chat on the bus.

(In my opinion and experience with this kind of communication) -
I don’t think in this kind of configuration you can disconnect all the buses to isolate the problem (unless there is a short). There has to be a line of communication for request and responses. You might be able to drop a slave off the bus, but having seen you list of problems, it looks like the master could be giving you the trouble.

 

Thanks