C41977

Went to help a friend today. No Start/Crank problem on his 92. I brought my OTC Genysis with me. Checked all fuses, all good. Jumped starter at sterter and turns over. Left side of dash does not light up, neither does odometer (no security light). Scanner got into the ECU with no problem but would not read when I tried accessing the CCM part. The VATS is already bypassed and I checked the key and the bypasses VATS and they both read the same, 7.5K ohms. I can't seem to find the Starter Enable Relay and from what I can tell, it powers up the CCM. I found a couple of relays on left side of dash, next to the flasher but from my book, niether is it. One has 3 large yellow wires, the other relay has 2 large pink (same terminal) wires. Problem is the wiring and part locations seem to change for different year C4s. If it was an earlier model I could find the relay behind the center console near/above the radio. This stinks. Any help is appreciated.

P.S. We have spark, no injector pulse.

RACER 1993

The CCM has more than one fuse. I don't think the start relay is on when doing CCM diagnostics because the key is just turned to "ON".

You might try just running the CCM diagnostics and see if the dash lamps and stuff work. Even if the display is not working it may turn the inside lights on, honk the horn, etc.

Find out if anything works that is controlled by the CCM

rodj

The CCM monitors various systems and reports faults.
The CCM send a data signal to the ECM to engage injectors.
On major systems , if in fault will not allow car to start.
SIR (airbag) faults will do this for instance.
Something as little as a bad earth on one of the motion sensors ( common problem )will give a error code and no signal to fire injectors.
The CCM will even display a code if you install an aftermarket stereo unless you put the correct resistor in the wiring circut.
Can you bring up the CCM codes on the dash display?

92LRC

the starter relay on a 92 is behind the drivers hush panel tucked up on the left side of the steering collumn. there are 3 realys there 1- starter 2- cruise control 3- bus delay.

I'm not sure if what you've got is a VATS issue or not but with these cars starting problems usually lead to VATS.

http://forums.corvetteforum.com/1558635223-post13.html

follow the link on this one to the 1990 starter enable relay. the location for the 92 is the same.
http://www.vatssucks.com/

http://forums.corvetteforum.com/c4-g...bug-fixed.html

gw962

To check the CCM diagnostics, ground A (top right) to G ( bottom left ) on the ALDL. Any DTCs should show on the Speedo display.

C41977

No codes in any system...and the Genysis can go into the BCM...I haven't taken a look at it until today. This is the strange thing: according to what I can find there should be some fuses by the battery (maxi fuses) I think but there's nothing there. The only fuses of any sort are on the passenger side. I appreciate the help. I'll report back!

RACER 1993

There is a fuse block above the battery and another by the master cylinder. The main ECM fuse is by the battery.

C41977

Well, whatever fuses where by the battery are no longer there. I know that sounds strange, but they're not there. There are 3 relays to the left of the dash and a place for 2 to the right. However, there is only one relay to the right in place. They're just regular relays and I thought the starter enable relay looked quite different from a reg. 5 prong relay.

92LRC

the starter enable relay is your standard "cube" type 5 prong relay. plugs right in like the rest of them

C41977

The starter enable relay must be on the left then. And it is clicking, what I'm going to try to dig up some schematics on it. Oh, forgot to mention the radio is still working fine...don't know if that has anything to do with the CCM.

C41977

We ran a ground wire to the black/yellow wire on the starter relay and the motor turns over but of course, it still won't start due to the injectors being shut down. NO security light flashing as engine turns over.

BluRay

I am not SURE about this, but it seems like they had fusible links in them. These of course are just black cylinders molded into the wires. Have you taken a volt/ohm meter to the system and checked for necessary power and grounds?

C41977

BluRay, where people say there are fuses we have a bunch of fusible links. We checked them and they were all good. I think I'm going to try to make that "jumper box" off of vatsucks.com for $10 of Radio Shack parts and it should by-pass or "trick" the ECM into think it's getting the correct signal from the module. It's a 5 volt signal but we can't put 5 volts to the wire constantly, luckily I found out the info. from that website. I hope it works! Changing that module behind the dash...makes me cringe! I'll keep updating. Maybe one day this info. will help someone else out. VATSUCKS

C41977

I had some internet problems after my last post. I sent the chip to TPIS and they got around the BCM...BUT as I guessed the car still would not turn over so I just ran some wires to the starter and now I just turn the key forward and hit the switch to start the vehicle. However, I have a BCM on back-order from GM and am getting that programmed as right now my dash lights still don't work (gauges do) and I should be able to turn the key over normally after that.

P.S. If I'd known the BCM was that easy to get to I might have just done that in the first place, I thought the whole dash had to come out. It's not bad at all. I hope this post helps someone else and PM if anyone needs any help.

jfb

I believe that you cannot simply connect a 7.5k resistor in place of the ign key pellet to bypass a 92 VATS. The later C4's require the ign key to go from out of the ign to in the ign. A permanent resistor bypass looks to the computer like the key is constantly in the ign. VATS bypass in later C4's require a 30 Hertz or 60 Hertz (can't remember which, I have an 87) signal to the computer if you permanently connect a resistor to the VATS module. Also, be aware that the resistor has to be within 4% of the correct resistor value. Analog ohmeters usually cannot measure a resistor within that tolerance.
I contend that it is much better to replace the ign lock which has new contacts that make connection to the pellet. This way you are protected from the 99% way cars are stolen, by bashing the steering column and jumping the ignition. The person I bought my 87 from, bought an 89 vette and one day they came out of work to find the driver window busted out and the steering column busted out, but the 89 hadn't budged an inch. Keep your car in good repair.

TopFuelVette

I am having trouble with my 94 Vette. I went down to start the car this morning. I opened the door and heard no ignition door chime when the key was inserted in the ignition. This confused me. I turned the key to start the car and nothing. No lights were on in the cabin with the door open, no starter sound, no mileage displayed on the digital display and the keyless entry fob would not operate the locks or any of it's other functions. There is also some sort of subtle clicking in the dash. I am not sure if this is normal or not but the car will not start.

What does work.
-radio
-exterior lights and some of the fault lights on the dash.

Any help is appreciated. I am really stumped.

hockeyhead019

Might have better luck starting your own thread with the problem. Start simple with battery voltage check.

TopFuelVette

Well.. I figured out the issue, It was the VATS. The VATS needed to be reset for some unknown reason. This had me really worried for a moment. I just didn’t understand how a car with 20,000 miles on it would have a BCM issue especially when it is just so rare of an issue to start with. Anything can happen I guess though. According to what I’ve read a VATS reset is supposed to take 8 minutes. Mine took over 20 minutes. It ran great last night after the reset.

Thanks Again,

Ricardo Moreno

I'm having an issue with my 94 vette it started and turned off right away and would not crank anymore I have the same symptoms that you mentioned, My LCD will not turn on and my interior lights are not working we were able to start the car by bypassing under the dash but will not stay running for more than 5 seconds. How do you reset the vats. I would like to try that.

Thanks in advance

TopFuelVette

To answer your question about reseting the VATS. I believe the VATS will reset by it's self in 8 to 15 minutes. I am not exactly sure of the procedure but I believe you leave the ignition in the ON position with the drivers side door open for 8 to 15 minutes.

Bypassing the VATS with a resistor or resistors might be a wise thing to explore. This is a fairly easy item to make yourself with some solder, shrink tube, used connector and resistors.

My issue ended up being the Body Control Module. I ordered a used BCM from eBay and went through the depressing task of taking apart my virgin cars console and replacing it with one with significantly more miles than my car has. It was heartbreaking to remove a BCM from a car with 24,000 miles on it only to replace it with a one that reads 102,310 miles. I am in the process of sending my original module out for repair to Davies in North Carolina. I hope Davies can fix my unit. It's an utter crime that GM no longer makes BCM's/CCM's any longer for these cars. This is a frustrating process to say the least and not super easy to diagnose as symptoms are misleading if you do not know what you are looking for. I miss the good ole days of carbs coils and points, not two to three computers communicating with each other in some weird relationship that are placed in areas that not even a midget contortionist can reach. This process is a month in progress and probably another two plus weeks out before completion. All due to a BCM in a car with 24,000 miles on it... Well, sorry for the ranting and raving. I think I just needed to release some steam. LOL.