I have a '02 silverado 2500 Duramax. After Leaving the ignition key on overnight I tried to start it & got no response from the starter, but the alarm came on ( factory system w/ lights, horn, & siren) and will not turn off. Tried the lock/unlock buttons on the remote and key in the ignition, but nothing happens. The alarm continues and the engine does not turn over.
usually these alarms shut off in a few minutes to avoid draining the battery. This one doesn’t? At least the battery isn’t dead.
You say “key in the ignition”. Am I correct in thinking (I hate that other word) you turned the key to the ON position and then OFF again?
I test the security system periodically in my '02 Tahoe and when I set it off, I insert and turn the ignition key as I described to turn it off.
If the security system doesn’t shut off at that point, I would suspect it’s because the battery is dead to the point where it doesn’t have enough juice to send a signal to the computer.
Was this battery new or the original? If original, being 5 going on 6 years old, you may want to replace it. Make sure there is no parasitic drain though.
Have you removed/cleaned and replaced (wrench tight) both ends of the battery cables?
Corrosion has a tendency to build up under the positive connection plastic cover.