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Welcome, I'm Chris (aka Moose) I prefer to work when others don't, I am here around lunch and after dinner till after midnight.
Is this the scenario. You exit the vehicle, lock it. Later on the horn and lights are pulsing?
Any current trouble codes?
A low voltage code can cause this, which is why I wanted to make sure there are no codes now.
When you press the panic button do the lights flash?
Any aftermarket electronics on the vehicle?
While driving do you ever get a false door ajar warning or the courtesy lights coming on for no reason?
Since there are now no codes, no door ajar issues, no battery concerns.
I would check for a hood closed switch that is out of adjustment.
Diagnosing this system is tough when the perimeter theft system goes off. Sometimes locking the vehicle and then 30 minutes later push and pull on each opening will trigger an alarm and tell you where to look. Sometimes you have to hook up a volt meter to the power outlet with a video camera to watch it and inside the cab to see what is happening.
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That would be included in the comment I made on "push pull on each opening"
Yes this is a possible cause but I would expect a warning light when it falsely shows open while closed and driving.
Trust me this is a hard issue to figure out, as you can see from the prior shops giving in.
One thing I forgot to mention. This alarm goes off when it sees a voltage drop. It thinks someone has broken a window, reached in and opened a door. So any sudden voltage drop will cause this.
Hello again Chris here,