Gregga55

Long time reader, first time asking for help! Haven't drove my 94 Vette all summer, (LT1 6 speed) been through 3 used BCM units, can't seem to get any to link up, thinking about just having mine rebuilt because GM doesn't even sell them. My Vette will start with the current BCM, but if I drive it down the road and shut it off, many times it wont start, But, wait for 30 minutes and then it starts. Corvette shop told me my BCM was going bad and wanted $1200, I thought..Noway!! me and my buddy that knows car pretty well can do this! I have bought 3 used ones that appear to be the same as mine, won't link up! Nothing happens, except I can read the milage of the BCM I am trying to install, so I put the old one back in, fires up and runs great!!....Except I keep getting stuck places! I heard there was a forum where others have had this same problem which took years to figure out???? My buddy now thinks its the passive restraint system??? Just wondering if anyone has had this same problem, or could head me it the right direction. Appreciate any insight, I have seen so many problems solved on this site!

Hooked on Vettes

When the problem occurs you need to verify what is missing.
Spark or fuel.

Not likely the problem is the BCM (Body Control Module)
also called the CCM (Central Control Module).

When you purchase a used BCM/CCM you need to know
what key pellet resistance value it was programmed for.

When the key pellet is read properly by the CCM when you
turn the ignition switch to On, the Security light in the dash
cluster should go Off. If it stays on, that indicates the
key pellet resistance doesn't match what the CCM was
programmed for and the starter will not engage.

To find the correct resistance value is found by trial and error.

Gregga55

that all makes perfect sense, because the security light stayed on, I am beginning to believe that I got bad info from my Corvette shop! I remember that when he tested both of my keys (he had this little tester box that he put the key into), the pellet in them both were not very good, but he said they both worked, maybe put old BCM back in the car, and have a new key made and see if that solves the problem? Any other ideas? Oh thanks for the quick response!

Hooked on Vettes

What do you mean won't restart?

Engine won't crank?
Security light stays on?

If the Security light stays on that indicates the key pellet wasn't
read properly and a lock out period of around 4 minutes takes place. During this time if you try to start the car again the
time out period starts again.

If the key pellet is good most likely the ignition key cylinder wires
are bad. Every time you turn the ignition key cylinder the wires
twist and eventually break.



Most people take a resistor and place it across the two wires
going to the CCM that normally connect to the key cylinder.

Short either pin 4 or 5 to pin 12 on the diagnostic connector above
the drivers right knee. Turn the ignition On. Look at the dash cluster
LCD and see if any codes are set.

Module 1 is for the CCM.
Module 4 is for the PCM.

If any codes are set note what they are. Clear any codes, by disconnecting the negative battery terminal for a couple of seconds then reconnect.

Gregga55

Sorry it took so long to get back, drove my Vette last night, when I got home, it won't start, when I say it won't start, it doesn't turn over, clicks like everything turns on, lights light up but nothing, some of the light do stay on, the
Battery light, Service light and the airbag light stay on only. Tried waiting for 4-5 minutes and tried to start it again, still nothing, 20 minutes later, fired right up like nothing was wrong, it will always start if it has been sitting. Not so sure I can run the test that you mentioned, I have a buddy of mine that can. Wondering if it is the chip in the key, or the key cylinder. Thanks for your help, I will wait for your response, then I will probably buy a new key, and Key cylinder

smooth1990

Take a multimeter and check the resistance on your chip in your key. After you find the resistance go to your local radio shack and buy a small bag of resistors for roughly 4 dollars. Then you want to find some resistors that match up to the value of your key and solder them together. After That take the access plate off above your knees on the drivers side and look for a pair of wires wrapped in a orange coating like the picture depicts above. Unplug and Cut the wires that go up to the key cylinder threw the steering column . make sure you leave 3 inches or so of wires on the plug to work with. Then you wire, solder and shrink wrap your resistor pack into the plug. Then you can go out and plug it back into the harness and see what happens. Doing this will tell you for sure if you have a bad key and cylinder. It costs maybe 5 bucks versus the labor and cost of a new cylinder. If its not a bad resistor/cylinder you can always wire it back together with no harm done.

My wires for the vats went out/broke and i could not start the car at all. I personally dont think this is your issue but for the 5 bucks its worth a try. good luck to ya.


check out this video or search youtube for others.

Gregga55

If it's not the BCM or the key and key cylinder, what might it be?

Deakins

Do you get any sensation of the starter or solenoid trying to function at all after you drive it and it acts up?

Gregga55

No, it either starts or it doesn't, I just drove it to my office, turned it off and then started it, fired right back up twice and the 3rd time it didn't. Turn the key, no battery or starter noise at all, lights come on and then go off except for the Battery light, Service light and the Airbag light stay on. But I let it sit for 20 minutes and then it will start. It always starts after sitting!! But only 50% chance of it starting after running, wether it is running for 1 minute with no time to warm up or an hour after its hot.

Kevova

Keys almost never go bad. Dealer has a tool which reads keys and analyzes cylinder. Tool hooks up in key circuit. key code with key in cylinder should match code when key is inserted in slot in tool. When key is turned code should not flicker. It is possible cylinder is on it's way out. If it passes test - key /cylinder not the cause. Starter enable relay is another common cause. Other possible poor battery connections, poor grounds, clutch switch adjustment, starter.

Gregga55

OK, thank you for all of your quick responses, My vette started up after work and I ran it hard on the way home, raced an SUV and a Mustang, LOL!!! Why do people always want to race a Corvette when they know they can't even come close??? Anyway, got it home and it won't start, checked the lights that stayed on, and the security light does stay on, as the air bag light flashes and goes off, but waited 20 minutes and it fires up…..so OK I will take the info I have gathered here to a couple places and see what I can come up with. I appreciate your help, Thank You