The VATS bug jumped up and bit me Friday. Spent the weekend troubleshooting.

1. Jumpered A to G to pull CCM codes. H51 shows up ( VATS ).
2. CLeared codes, shut off key and tried again. C12 on the display.
3. Cycled to 1.2 module and checked # 6 for the key code per the FSM. It came up 223, which is out of range for all codes. (Mine should read a max of 156.
4. Pulled the connection and ran a crude resistor jumper which gave me an inconsistent 154. It won't stay there, so my jumper needs work.
5. Followed the FSM tree and tested the B connection from the CCM. The book says 4.95 to 5.05V. Mine reads 4.93V.
Will this lower voltage affect the resistance the CCM reads from the key or jumper?

Of course, the FSM states that a voltage out of range requires backprobing the W5 terminal of the CCM to check continuity, so this evening I get to tear apart my interior to get to the terminal.

On a related note, I checked module 1.4 and the key in ignition indicator showed no key. While wiggling the key cylinder ( FSM testing technique), the CCM would show the key in place, or no key, depending on the position of the wiggle.

I'm also going to pull apart the steering wheel to replace the lock cylinder since this shows to be one of those famous intermittents, but I guess the main question has to be the CCM.

Has anyone else had to dig into their CCM or had this type of issue?

Thanks

 

You should really give the year of your vehicle for assistance.

As an example, the '95 LT1 CCM is known to have some issues that affect starting, where other years are not as prone to the problem.
And, I think the late L98s had CCMs too.

Tom Piper

 

D'oh!!!
I knew that....it is a '90, Auto Coupe.

 

It seems you may have gone "a long way around" to get to a possible VATS issue. You don't need to pull apart the column to check! Do you have maybe a couple keys? If you've got a couple keys check both for the resistance of the chip on the key. If they match or are within the "range" required you can just remove the connector for the harness from the cylinder at the bottom of the column insert a key in the cylinder and check for matching resistance at the connector. If it's a "no match" or if you can wiggle the wire and the resistance "fluctuates" you're onto the VATS issue.
The correct fix would be to replace the cylinder in the column and that will require keys to match the tumbler of the new cylinder but the resistance of your key(presently)!
This is a very quick check, minimal disassembly and only requires a
DMM and it sounds like you've got one.
There are other "short cuts" and "theories" for the repair.
The search for VATS issues on this forum should get you several "solutions"! I just offered the "more likely" and easiest way to confirm! Or at least I believe so! 30 minutes and you'll be at least past a "simple VATS"

Google GM VATS for lots of valuable information! The VATS values etc.! Good luck!

 

Thanks.
I have checked the keys and both ohm out correct. The key switch is loose and not giving me consistent ohms on the wiggle. That is why this will be my first repair.
What concerned me was the strange numbers I'd get on the CCM / dash display, when I know the ohms are correct. The voltage being .2v lower than the FSM min spec raised a small flag.
I would much prefer to change the lock cylinder than the CCM, even though fooling with the air bag gives pause.
Thanks for your reply

 

You can do this if you want to confirm it's the cylinder since you want to buy it anyway! Buy the cylinder and connect it to the harness at the base of the column. Use one of your keys and just insert it in the cylinder, no need to rotate. You should now have answered the VATS request. Using your other key to rotate the cylinder the car will/should run. Stuff the cylinder up under the dash until you're ready to do the column thing.
Air bag isn't that big an issue!

 

A quick update....
With the tilt steering in the up position, the car starts. In the down position, no start. Definitely a crimped wire or loose connection. Cylinder replacement here we come.

Also found that there is a key input signal to the CCM by digging through the schematics in the FSM. This is probably why my temporary resistor bypass didn't work. Just like me, the CCM was confused by a correct resistor signal, but no key input.

Hope this helps anyone with similar symptoms.

Also, thanks for the replies and ideas.

 

Additional update:

Hopefully this can help others...
I swapped out the lock cylinder because of a "no key in ignition" indicator( chimes, etc)
This made no difference to the CCM. It continued to show a value from 209 to 226 on the VATS A/D count on the diagnostics readout.
I started to disassemble the interior to gain access to the CCM to backprobe the connectors.
During this, I was able to get my fingertips on the connectors and "wiggle" them. This changed the VATS readout to 154, which is in the acceptable range for my key. I waited 4 minutes and she fired up.

I ran some errands Monday and had a no crank incident again. I tapped on the CCM frame with a pair of pliers, waited 4 min and she cranked and fired.
I'm not sure if I have a loose connection or questionable CCM interior ground yet, but I should be on the right track. Just some additional disassembly and I should know.