Last week I changed the ignition lock cylinder,but I used a second hand one from another car but I forgot and used the security part as well. The car would not start and the alarm went off. After much reading of the manual I discovered there is a security code in the key head which also unlocks the doors which is read buy the BCM via the metal strip on the outside of the lock cylinder. Then I discovered the battery in the key head was flat & that there was an open circuit inside, after a new battery and a solder job the security alarm was reset & the car started.This only took me 2 days. Give me a HQ any day.