Thisguyuknow

Hey guys I am only a lurker on here because I am a Jeep owner. Planning on doing a vette 350 swap in my Jeep and am going over the wiring. I got a complete engine and underdash harness from a 1990 vette part out. In the schematics there is a pass-key module.

I assume this is an anti theft module that will not cut on the fuel pump if the key is not in the ignition? Can it be bypassed? If so how?

eutu1984

Do a search on VAT bypass for a 1990 corvette, you should find lots of info.

Hooked on Vettes

When you turn the ignition On the key pellet resistance is read by the
CCM. If the resistance matches what the CCM was programmed for it
does two things.

Grounds the Starter Enable relay primary coil to complete the 12 volt
path to the starter solenoid. You can jump/remove the Starter Enable
relay from the circuit or if you keep it you ground the primary relay coil
and enable it all the time.

The CCM also sends (I think it's a 30 hz square wave signal for the 90
L98 and 50 hz for 92 LT1's) to the ECM so the ECM will pulse the injectors.

You can purchase a module to do this that does both 30 hz or 50hz.
You connect the 30 hz signal to the ECM Red connector also called
connector B pin 6 Dark Blue wire called Vats Signal circuit 229.

http://www.ebay.com/itm/GM-VATS-or-PASSkey-II-Bypass-Module-For-LS1-and-LT1-/271223021636?pt=Motors_Car_Truck_Parts_Accessories&hash=item3f2626e044&vxp=mtr

The ECM Eprom needs to be reprogrammed so a Vats diagnositic error code doesn't set since the CCM will not be used.

Thisguyuknow

Great that is exactly what I need. Looks too easy just snip the starter relay wire that heads to the ccm and ground it. Then add that module you linked... So even with that bypass module I will still need to reprogram the ECM? Will the ECM run the engine fine just throw a code or will it not operate until I reprogram to ignor the CCM error

Hooked on Vettes

That's an interesting question.

The CCM is what normally sends the square wave signal to the ECM.

The ECM can set code 46. Vehicle anti theft system Pass key circuit.

From the service manual.

The Vats Pass Key system is desigend to disable vehicle operation
if the incorrect key or starting procedure is used. The CCM sends a
signal to the ECM if the correct key is being used. If the proper signal
does not reach the ECM on Circuit 229, the ECM will not pulse the
fuel injectors ON and thus not allow the vehicle to start.

Code 46 will set if the proper signal is not being received on Circuit
229 by the ECM, when the ignition is turned ON.

Code 46 does not store in the ECM memory but is only present when the conditions stated above are met.

In normal operation, if the proper key pellet resistance is not read,
the CCM begins a lock out period of about 4 minutes where the
engine won't crank nor pulse the injectors.

This lock out period can't be reset even if you disconnect the battery.
If you were to turn the ignition off and then on again and try to crank
the engine the lock out period would start over.

Since you won't use the CCM or the key pellet, there would be no lock out period. All you need is that squate wave signal to the ECM when the ignition is turned on.

Bottom line it appears you don't need the Eprom reprogrammed.