Hi everyone, hoping someone can help... 1993 corvette lt1. Car won't crank won't start. Been through all diagnostic steps from service manual. The problem is with the start enable relay ground. I can start the car by manually grounding the start enable relay. Anyone know how to fix this problem? Thanx in advance...

 

If the engine or trans was removed, verify all the ground wires were re-attached.

From the negative battery terminal cable one cable goes to the frame.
From the frame there is a braided cable that goes to a stud on the driver side of the bellhousing.

G106 is the ground for the CCM. It's located above the oil filter.

I recall Gordon Killebrew who was a GM tech support person for the C4's mentioned some of the 93 CCM's did have a problem grounding the starter enable relay. He recommend grounding the primary relay coil to enable it all the time. This doesn't cause any problems because you still need the correct key with the proper resistance to enable the pulsing of the injectors.

If you decide to replace the CCM with a re-manufactured one you need a Tech 1 to program it. You could buy a used CCM but would need to determine the key pellet resistance it was programmed for by trial and error. The odometer reading on a used CCM can not be changed.

 

Hey, thx for the quick reply. There's another issue now, I have the relay grounded to a random spot on the frame, and it cranks now but won't fire up. If it does fire up, it dies after a second and only cranks. But before I grounded the relay, it didn't even crank

 

Here's a little history. Car sat for yrs... Started it one day and it ran for abt a week. Then got all these check engine lights, car ran really rough and would die out and not start up again. Idle was very rough at best. Ran the dtc codes and eventually changed MAP sensor, MAT sensor, and serpentine belt. Changed the oil and cleaned the intake manifold. Then added seafoam to the gas tank. That really helped it, but car was still not running great. The sys warning and check eng light have always been on. Changing the serpentine belt finally turned it off, but the sys warning still persists. One night the dash flashed on and off and the car was dying while I was driving (dying and coming back on). Finally figured out that both bolts on the battery terminal were severely stripped. I changed the bolts and all the probs went away. The car ran like it was brand new, only prob was sys warning never stopped. But I drove for over a month without issue. The other day, I parked it and that's when it wouldn't crank. Towed it home, diagnosed it. Trouble shot everything until I discovered the start enable relay. As I mentioned above, when I manually grounded it I got it to start. But now it just cranks. But won't crank unless manually grounded. Again, thx for your help. Hope this extra history helps

 

In your first post it did sound like the problem was with the CCM.
Now with all the other information

There are two things the CCM does when you insert the key and turn the ignition to On.

You should see the Security light in the dash go on then off.
If the Security light stays on solid, it indicates the key pellet wasn't read properly. A three minute time out period begins where if you try to start the car again the time out starts over again so you have to wait for the time out to expire.

After the key pellet is read properly, the CCM grounds the starter enable relay. It also tells the ECM to pulse the fuel injectors.

If you manually ground the starter enable relay and the key pellet wasn't read properly the fuel injectors won't pulse so the engine won't run. (Could run for a second).

If SYS is blinking there is a CCM code set. Module 1
Service Engine soon indicator on, indicates a ECM code is set Module 4

Pull the codes by shorting pin A to G on the diagnostic connector, turn the ignition On and look at the speedometer LCD. Post what the DTC's are.

 

Hey thanks for the info... I did the key test and the security light does stay solid! Any suggestions on where to go from here? Thanx in advance

 

Also ran ccm codes, h53, h63 module 1. I also checked the enable start relay and ccm says no prob.

 

No current codes in module 1 just h53 and h63...

 

Both codes indicate problems with the reading of the key pellet.
1) Worn or dirty key pellet
Solution:
With an ohm meter measure the key pellet resistance and get a new key cut.

2) Worn key cylinder contacts.
Solution: Replace the ignition key cylinder or bypass the key cylinder by disconnecting the two wire connector at the base of the steering column and place a resistor with the proper resistance across the two pin connector going back to the CCM. Using this method makes it easy to steal the vehicle.

Below is a picture of the ignition key cylinder, a chart showing the values of the 15 key pellet resistance values and a link showing where you can buy the resistors.





http://www.ebay.com/itm/Directed-652T-Resistors-Pack-General-Motors-GM-VATS-Override-Bypass-Kit-/291175559371?pt=US_Car_Keys_Transponders&hash=item43cb6a70cb&vxp=mtr

 

Can you not just bypass the key pellet with a resistor of the proper value in the harness to fake it out? I have done this on other GM's as where the cylinder was more times the problem than the resistor key itself. Or does it look for something else and throw a code/check engine light?

 

But using that method the starter enable relay and the pulsing of the fuel injectors are always enabled. All a thief needs to do is break the key cylinder and use a screw driver to start the car.

 

Thanks for the info. I bypassed the VATS and car fired up instantly. Running like new again. Only prob is SYS warning still blinking.

 

I followed your suggestions and car fired up and ran smooth. Thanks a million

 

Great info, thanks. This solved my prob

 

You need to clear the codes. Disconnecting the battery will clear the codes.

All you've done is bypassed the Key cylinder that reads the key pellet
You don't want to keep the Starter Enable Relay grounded which is probably causing the SYS.

Remove the ground wire and the SYS should go away.
.

 

Which ground wire? I already removed the manual ground I had rigged up for the start enable relay

 

If you still get SYS after you removed the ground from the starter enable relay. You need to pull the codes again. Module 1 should show an error code. If you see a Code 72 it's because of an aftermarket radio.

If no error code is displayed for module 1, that usually indicates your battery charge is low.

 

I recently installed a new stereo system, will run the codes again. But I never got 72 before. Is there anyway to clear the light with this new stereo? I just noticed that the dash seems a little dim, would that set the sys light off too? Thanks again for all your help.

 

When you replace a Bose radio, you remove the pull up resistors for the dimming circuit. The CCM does a power up diagnostic on the dimming circuit. Because the voltage is not correct it usually sets a DTC 72.

http://www.corvetteforum.net/c4/dave8476/index4.shtml

Dash light brightness during the day with head lights off is adjusted automatically by the photo cell in the Driver Information Center. With headlights on or in Park position it's a combination of the photo cell and the dimmer switch. Shine a flash light on the sensor and the lights should get brighter. Place your finger over it and the dash lights should dim.