1994 C4 no crank no start with vats bypass
 

Hey all,

New to the forum. I usually don't sign up for these, but I am really stuck.

I have a 1994 C4 Manual transmission.When i bought it, there was intermittent display on the dash. I went ahead and started some modifications to the system and then the car went into start it and No crank/no start.

Modifications were:
-Ac/heater coil removal.
-disconnected electrical and took doors off to paint.

When I put everything back together i didn't have a security light and i started with this issue. I am wondering if i am missing something or i faulted the BCM/CCM and how i would reset that.
I purchased the eklers bypass for my key and it is currently hooked up. I have disconnected the battery for hours and reconnected to try and reset that way. I have the airbag warning light, coolant warning light, and low tire pressure lights on when i turn it on. All fuses are good and all lights/horn work.

Any help would be appreciated.

Thank,
Jack

Any codes being set?
https://tech.corvettecentral.com/201...trouble-codes/

Thank you for the response. Nope no codes. I cannot even get the LCD screen to show anything. No odometer no codes nothing. Plugged my nexas scanner in as well and couldn't get power to that unit.
When i turn on the car this is what i see.

Bummer, was hoping to see codes to get a starting point. At this point I suspect an issue with connections to the CCM, but not necessarily a problem with the CCM...especially if the car started before you did the work.

Since you said you removed the heater coil, I suspect damage to a wiring harness or maybe a plug to CCM got pulled lose in the process. I doubt removing the doors would cause the issue.

It might be time to consider picking up a set of Factory Service Manuals which can be an enormous help when trying to troubleshoot something like this.
https://www.ebay.com/sch/i.html?_odk...nuals&_sacat=0

Hey BAC22,

Thanks for the help. Yeah that is the only thing i can think of as well. Maybe Messing with the wiring harness somehow faulted the ccm. I was hoping hooking up a scanner would read something out.


Thanks

First off get rid of the VATS bypass for now because it's just introducing additional variables.

The CCM drives the speedometer display and also reads the key resistance for VATS. If it is satisfied, then it closes the start relay to crank the engine. In addition, the CCM has to be operating to tell the PCM to turn on the injectors (FEDS) and ignition spark during cranking.

The door switches do relate and activate the security light which is controlled by the CCM . However the door switches would not affect the engine from starting if all is working normal and I can tell you it's not.

Your root cause here is the CCM not working probably causing all the other problems. Somehow it seems not to be powered up by possible some wiring that might have been cut, pinched or a plug not connected. You can't say you don’t have any codes because the CCM is the master of tracking the codes and outputting them whether you use a OBD1 scanner or the on board diagnostics. (Forget codes, it will not aid in fixing this problem).

You have to find out why the CCM is not working by looking in the areas you were working in. Keep an open mind and there are several CCM fuses (#16, 35, 39) make sure they are good. If they are, the wiring may be the problem.

Check to see if there are 12 volts on those fuses with the key on. Use a pin to get in there for the measurement and find a good ground.

I am getting proper voltage, and wiring is fine i the area. I double checked the door wiring to make sure i didn't pinch a cord going back in. Speedometer wasn't working prior to the work but the car was running fine.

Update however: I pulled apart the center console and trashed the ac unit and stock stereo (didn't work anyway) and now I can now get the car started if i put the key in and turn the ignition really quickly. Maybe the CCM didnt like reading the ac signal with no ac unit? If i leave the key in for a few seconds I will get 1/5 times to start. The issue now is that it runs for 5 seconds and then shuts off. When idling it sounds fine. Fuel pump is still on after car shuts down. I will check fuel pressure tomorrow. Spark is white and strong. I have disconnected maf sensor and still same thing. Maybe still an issue with bad ccm signal?

If i buy a good ccm off ebay and my key is incorrect, can i still use the ccm and my key with a vats bypass?

Thanks

When it shut down you need to figure out if it is spark or fuel pressure at that time and you need a pressure gauge to do that.

The security light also indicates if VATS is activated as being on steady. Without the light working at all you are really in the dark. If VATS activates it will take about 3 minutes (varies) for it to reset before the engine will crank again and that’s if you don’t put the key in and try it. You have to leave it alone 3 minutes with key not turned.

Also make sure the ignition switch at the bottom of the steering column is not lose as the linkage too.

There is also a possibility the dash unit could be the problem of the speedo not lighting up and might be part of the security light problem also. You might take it out and give it a good visual check the connector and lamps. I can't say the CCM is not bad, but might not be a good investment yet.

I don’t know what the bypass kit bypasses. If it is just the resistance of the key it's just a substitution of the key pellet but VATS is still an active part of the system.

Getting a car with problems you don’t know what someone else has done and hard to give good advice.

OP - don't know how many components you removed and then reinstalled in the dash but if while doing it maybe you didn't get the connector to the DIC attached correctly.

There's an interesting thing going on in your 'KEY ON - NOT RUNNING' snapshot. Aside from the LCD not being lit if there were no tach problems the TACH I would have thought parked @ 0. '94s aren't known for tach issues so yours looks maybe odd.

You said all fuses were good and you've been advised to check all CCM related but maybe you need to check the LCD fuse also. Maybe a MAXI in the under-hood also.

VATS delay between attempts mentioned @ 3 minutes but I've seen that vary 1st hand, greater than 3 not uncommon. A wait of 5 is sufficient for a simple test.

Everyone Thank you for your help!. The issue was when i took the doors off the door closed switch that tells the car to turn off interior lights was not correctly installed. So this kept the lights inside the car on and killed the battery. I recharged the battery and pulled the interior light fuse. I put that back in and now the car stays on. I am not sure what exactly connects to that fuse, but it will not allow the car to run for more than a few seconds if that it out. I pulled the fuse and put it back in and pulled it again to make sure that was the issue and it is.

Again. Thank you everyone for your help!

Jack

That's great that you are up and running.
Can you please tell us what the fuse number is or the labeling for it ?
I assume it's from the fuse box inside of the door.
Thanx :)

It was the "Interior lighting" fuse. Box is near the battery in the engine compartment. https://cimg5.ibsrv.net/gimg/www.cor...a380d4f5c1.jpg

Well OK a lot of it makes sense now. That Maxi 20A fuse provides power for the LCD display as well as CCM fuse #2. Could possibly affected communication between CCM and PCM and maybe fuel pump but who knows.

There probably was no voltage on CCM fuse #2 in the driver's door which would have been a big clue as to check up the line. Those Maxi fuses feed multiple circuits and can cause various strange problems. There must have been a heavy momentary short to pop a 20 amp fuse.

I think the OP was saying he pulled the fuse to turn off the interior lights.

I think your right. A bit confusing, I'll leave it where it is. :)