Corvette CCM Reverse Engineering Anyone?

[-=Jeff=-]

the flash tool for these things never got well tested beyond my bench
definitely interested to see if it works for you

What wires did you have connected, meaning do I need to apply power to all the power pins?

[NomakeWan]

What wires did you have connected, meaning do I need to apply power to all the power pins?

You don't need to apply power to all of the pins as many of them are tied together internally. Please follow the pinout I posted a few posts ago.

But isn't the PASSkey Stored?

It is. But if the correct key is not "inserted" (that is, the correct resistance value is not applied between pins E12 and F5) then the CCM will not allow external devices to read those locations in memory. They will appear as blank data instead of the correct PASSkey data.

[-=Jeff=-]

at this point, it is probably easier to work through my harness to get he wires I want as all the connectors are there..

[-=Jeff=-]

I am getting data on the serial bus but having this issue:

Reconnecting to ALDL bus, please wait....
ERROR! The bus is still noisy (retry)...
ERROR! The bus is still noisy (retry)...
ERROR! The bus is still noisy (retry)...
ERROR! Could not become the ALDL bus master.
ERROR! Error reading segment 0[40]
ERROR! Could not complete read procedure.

how do I get it not noisy?

[NomakeWan]

According to the source code for flashhack, those error messages in that order will be sent if no bus master is found within 5 seconds, and yet there is still data on the line every half-second for three retries.

What is likely happening here is that you did not power up the CCM in the proper sequence, and so it is not sending the proper bus master heartbeat message (which starts with F0, and is the "CCM requesting the presence of external bus master" call).

On my wiring layout I posted earlier, you'll notice two of the entries say "when key is inserted into cylinder" and "when key is turned to run position." These mean exactly as I wrote. You do not connect them until the rest are connected. Then you first "insert the key" by connecting C11 to ground, followed by "turning the key" by connecting both E4 and E5 to +12V. Doing this should tell the CCM that it should run the power on sequence, which will start broadcasting F0 diagnostic messages. It's this message which Flashhack looks for in order to become the bus master.

If you just power the CCM up but don't follow the correct sequence, it will broadcast its normal status request messages ($40 and $10) but will not broadcast the bus master request message (F0).

[-=Jeff=-]

Yeah that is.. lol, I was going to add switches, now I will have to.

Also turns out I think the 3 spares are 1-1990, 1-1991 and 1-1992

Will know when I get them scanned

I also have a harness to connect the cluster in my bench

[-=Jeff=-]

I still must be doing it wrong.. here is what you had earlier:
GRAY Connector
C1 Ground
C11 Ground (when key is inserted into cylinder)

GREEN Connector
E4 & E5 +12V (when key is turned to run position)
E12 to F5 PASSkey Resistor Value (VATS)
F1 +12V
F12 ALDL

SO, do I apply the 12v Last?

Right now my sequence is:

F1 - 12v C1 GND
C11 to ground
E4 and E5 12v
then try ALDL

I don't have the VATS code for this unit

[NomakeWan]

I still must be doing it wrong.. here is what you had earlier:
GRAY Connector
C1 Ground
C11 Ground (when key is inserted into cylinder)

GREEN Connector
E4 & E5 +12V (when key is turned to run position)
E12 to F5 PASSkey Resistor Value (VATS)
F1 +12V
F12 ALDL

SO, do I apply the 12v Last?

Right now my sequence is:

F1 - 12v C1 GND
C11 to ground
E4 and E5 12v
then try ALDL

I don't have the VATS code for this unit

Disclaimer that I haven't bench-tested one of these units, and when steveo bench-tested his, he had an ECM to plug into it and had the ECM reprogrammed to send a specific bus message to make the CCM happy. I personally don't believe that's necessary because a reman facility likely wouldn't have that available. So I believe the issue is in the sequencing.

That said, your sequencing looks correct for what I would assume is necessary. It is possible that not having the right PASSkey resistor value is causing this issue, but the documentation for the 1990 CCM seems to imply that you will still be able to query the CCM, you just won't be able to access the memory locations that store PASSkey information.

I won't be able to test it right this second, but likely tomorrow I may be able to test idle data messages on a CCM without the appropriate PASSkey and no ECM on the serial data bus. I'll just unplug my ECM's blue connector and then unplug the VATS harness from under the steering wheel, then turn the key to run and watch the idle messages.

And not having the right resistor isn't a big deal on a bench. VATS has a 4-minute timer. So try the resistance value for #1. Doesn't work, wait 5 minutes, then try #2. Rinse and repeat until you hit the right one.

To make it easier, you can connect a bulb to the security light output on the CCM. Wire the bulb between C6 and F2. If the security light comes on solid when you apply +12V to E4+E5, it's the wrong PASSkey and you have to wait 5 minutes. If the security light doesn't come on at all when you apply +12V to E4+E5, you found the right value.

Aren't GM cars great?



EDIT: Try killing the ground signal to C11 at the same time you apply +12V to E4 and E5. Had a look at my FSM as a sanity-check and in fact the C11 ground input states, "Key-in ignition switch is grounded with key inserted and ignition in 'off' or 'accessory' position" which implies that it will not be grounded when the key is turned to 'run'.