2003 Chevy Monte Carlo. I replaced the PCM with a new one. had it programed and did the relearn procedure twice, car still will not start. When I did the relearn no telltale signs of the security showed.I put a PCM in from a different car and I can start the car but no gas gauge and trans shift points all wrong. When I did the relearn on used pcm the ringer went off the entire time, but no ringer with new computer. PLEASE HELP THANKS.
Answer: You did not specify the reason for the PCM replacement. Was it to fix a no start problem?
Assuming the new PCM was a new factory, and not an aftermarket, and it is the correct part number, the theft system and indicator is controlled by the BCM, not PCM. The chime should not be on when relearning theft system- this is also controlled by the BCM. Sounds like you have a BCM problem, or a more common problem with the theft system- the Passlock sensor / ignition cylinder.
Shift points are controlled by PCM with what is called "Adapts". Basically it learns the way you drive to set shift points for best shift. A new, or used computer would need time to relearn shift points. A used computer may not have same programming for your car, which can cause all sorts of problems.