GM-GMC: starting problem, chevrolet z71, valet mode

Question
I drive a 1989 chevrolet z71 p/u with a 5.0 v8 engine. There is a anti-theft device in which you have to type in a code to start the vehicle. In valet mode or when disarmed the device will not enable the truck to start - (intermittent). any ideas?

Answer
I can tell you that if it needs a code it was installed aftermarket and the best thing to do is disconnect the device or take it to the place it was installed if you know.

If you are the second owner and you don't know take it to a place that you trust and have them find the brain of the device or where it is attached to in the vehicle and disconnect it.

At lot of times when an aftermarket alarm is placed in a vehicle the computer doesnt recognize this device and as the vehicle or device gets older and has trouble the vehicle will do strange things intermittantly and once the device is disabled be fine and other times the aftermarket devices do permanent damage. Since this is not a GM product and was installed aftermarket ( or after the vehicle was manufactured) I have no way to trouble shoot for this problem other than getting it somewhere to have it disconnected.

Sorry I couldn't be of more help.