GaryDoug

Can someone tell me the pin number (Cxx, Dxx, Exx, or Fxx) of the "LCD Data" connection at the CCM? It is a gray wire. The only diagram I have does not show that pin number.
Thanks

Hooked on Vettes

LCD serial data is pin F16 on the CCM Green connector.

GaryDoug

Thanks you very much. I see you have the same diagram with the missing information, but I did not have the other pages. This will help a lot.

I am trying to determine if the CCM I have is working or not. I am the author of Scan9495 and have tried unsuccessfully to make the app fully reliable for the Y-car of those years. So, I bought a defective CCM for cheap, fixed it (I think) but am having trouble getting a Tech 2 to talk to it. This will help me see if at least the cluster data is working to some degree.

Does anyone know if it must be connected to a Y-car pcm in order to connect to it?

Thanks again
Gary

Hooked on Vettes

To get the CCM in diagnostic mode you ground either pin 4 or 5 which are both ground to pin 12 on the diagnostic connector. Turn the ignition On and the CCM runs a self check then polls the PCM, EBTCM and the Derm for any DTC's. It displays the information on the LCD. After the DTC's are displayed it goes into a wait mode. You can then use the Driver Information buttons to navigate what you want the CCM to do.

What kind of test setup do you have?

The CCM flashes a SYS on the LCD when DTC's are set.
It communicates with the other modules via the serial bus circuit 800 which is a piece of wire.

GaryDoug

I only have the 95 CCM, no pcm or gage cluster. I wanted to see if there was serial data for the cluster coming out of the CCM, and there is. Of course I can't see a display and may not be able to decode the string of data, but at least I know that it is doing something. The CCM I bought was defective and doing nothing until I replace a defective part on the circuit board. Next step may be to see if this CCM will actually work in a car. I may have a couple of volunteers to help with this if it isn't too much work (or risk).

I am not too interested in the diagnostic mode used to obtain trouble codes, but rather to communicate directly with the pcm without any conflict with the CCM. If I can do that, I can modify the Scan9495 pc app to include Y-cars as well. And maybe get the CCM and HVAC data also.

I do have a 94 F-car pcm, ABS, and SIR module in a test bed, which were the ones used to develop the Scan9495 app for LT1 F-cars. So I am familiar with the silencing techniques that have to be done before I can get reliable data out. The problem with adapting the app to the LT1 Y-car is that the connection is only about 95% reliable due to some conflicts with "housekeeping" data on the bus, which I assume is coming from the CCM. Since I had no Vette modules, I have tried to debug this remotely with a Vette owner by sending him many trial versions of the app to try. Those versions included many attempts at silencing the PCM and CCM. So far, that technique has not been completely successful. Obviously a module is still sending data on the bus and I am not sure which one.

The scantool (a Tech 2) is used to communicate as a standard with the modules, but the Tech 2 halts when told to get the datastream from the CCM as if it is waiting for something. I do see data being sent from the CCM continuously but don't know exactly what it is saying. I have a data sniffer/recorder that I programmed to record anything on the bus. The Tech 2 will not send anything to the CCM until I break the connection and then it sends a CCM data request about every second, which would be normal for this scantool when disconnected temporarily. I have tried sending the data requests from my test bench setup directly but the CCM just ignores them. I wish I knew what was causing the Tech 2 to wait and what the CCM might do if there was a matching pcm attached. I wonder if the CCM refuses to accept any requests until after some kind of initialization with the other modules? My F-car pcm will not work with the CCM, so it is of no use.

My shop has the usual set of tools for a retired electrical engineer, like digital scope, power supplies, soldering stations, etc.

Hooked on Vettes

I was under the impression the 94-95 F car LT1 PCM could be flashed with a 94 or 95 Corvette bin and it would work in a Corvette.

GaryDoug

That is probably true, but I am not about to try it. Nor do I have the software/hardware to do it. Maybe if I can pick up a spare pcm somewhere cheap.

This app is just a hobby for me and I charge nothing for it, so I need to keep the costs down to keep it fun;-)

Hooked on Vettes

I did a test using a 90 Corvette which was the first year for the CCM.
I disconnected the four connectors on the 90 ECM.
Attached the Tech 1 cable to the OBD 1 connector.
Turned the ignition On.
Using the Mass Storage cartridge in the Tech 1 configured it for a 90 Corvette.
Selected CCM.
Message waiting for data continued to be displayed.

So it appears the Tech 1 cannot communicate with the CCM until it does some hand shaking/data exchange with the ECM.

GaryDoug

Wow thanks! That pretty much confirms my suspicions. Fortunately I found a volunteer who is willing to swap mine with his and use my Tech 2 so I can know if it is good now. If it is ok, I may buy another pcm and flash it to a Vette bin the volunteer can send me.

Thanks again. I will let you know how this unfolds.

GaryDoug

Can you provide some details? I have contacted 3 places that do pcm programming. Generally they say it works for engine swap application, but may not work in an actual 94 Corvette. I am getting the impression that the hardware differences may not allow communication with the other modules. Or that the OBD2 features will not work. Does anyone here know for sure?

Hooked on Vettes

The 94-95 Corvette used the 16181333 PCM.
I have the pin outs for the 4 external connectors.

If you have the pin outs for the F body 94 PCM you could compare the signal pin outs to see if they are the same.

GaryDoug

That would be nice. The pages in tabular form (just 4 pages) instead of the schematics would be best. I do have the 94 and 95 F-car service manuals. I do know that there is an OBD2 line from the pcm that does not exist on the F-car, but that shouldn't be too important because it goes nowhere but to the DLC. And there is an oil temp sensor that the F-car does not have but may have the input for it. I will test for that on my F-car setup. Thanks

GaryDoug

This is one of the responses I got today. The other 2 did not know anything for sure.

"From what I understand, the Corvette specific 16181333 PCM had one additional microchip for OBD-2 specific functions (possibly only used for OBD-2 communications, which you probably don’t need).

I know I’ve put 1994 Corvette programming on an 8051 PCM before – and I never heard back from the customer saying he had problems with it.

Ryan Gick
Sinister Performance, LLC".

Hooked on Vettes

I think I compared the PCM's a while back and the only thing different in the pin outs was the Red connector Pin A25 was labeled FEDS (Fuel Enable Disable signal) on the F body and not labeled on the Y body.

GaryDoug

Thanks for the documents. I will study them thoroughly. If you ever want access to many F-car factory service manuals including the 94, you can download free copies here: https://www.mediafire.com/folder/40m...y_files_folder

As far as the FEDs signal is concerned, it's probably not need by the Y-car because the CCM, which handles that function, is on the computer bus with the pcm and can send that signal to the pcm via the bus. On the F-car, the module handling the anti-theft features is not on any bus with the pcm and needs to use a wired connection.

GaryDoug

Well, my friend with the 95 C4 checked out my 95 CCM and it did work as far as he could tell, however it would not talk to the Tech 2 even when installed in his car. The Tech 2 would talk to the original one in his car. So I guess there is something wrong with my CCM. So I gave up on that CCM and bought another one, this one presumably good. But the Tech 2 still won't talk to the CCM or the ECM, so now I am lost again. I wonder if it is possible that nothing will communicate unless all the modules are present and connected? Like for example the instrument panel gauge set, or the ABS, or something else. For clarification, I programmed a spare 95 Camaro PCM as a 95 Corvette one. I was able to communicate with the pcm as a Camaro but not as a Corvette when it was tested alone or connected to the CCM.
Does any of this ring a bell with anyone?

Matthew King

Doing a swap got the motor and trans form a 96 corvette and bought a 96 corvette cluster thinking it would be plug and play..
for fuel and speed I found that it goes through the ccm first can I buy a ccm and just pin it for fuel and speed and then wire it to the cluster and it work okay? Or can I get the digital read out to work a differnt way without the ccm? Or am I just SOL? Please help