Security light flashing and beeping

[johnc847]

The security light in my grandfathers silverado started flashing today and beeping fast. The weird thing is if you put the key in and turn it to on, or will stop. The truck will start and runs fine. But of you turn it off, the security light keeps flashing and it beeps fast. Anyone have any idea? Everything I've read on the Internet is something about truck won't start but his will.

[MikeNH]

Aftermarket alarm or remote start?

 

Year of truck would help too.

[gmtech4]

needs to be scanned first

[johnc847]

It's a 2002 2500HD diesel.

 

Nothing aftermarket. All stock with stock keyless entry.

[Carder09]

Sounds like the passlock is pissed for some reason. Something isn't communicating at least, it seems that way to me. Since inserting the key with the chip in the key is allowing it to disable. Removing it is not allowing to return to its original "secure" state. If it's like the Colorados, then the ignition lock cylinder must be replaced and a passlock relearn must be performed. Not sure what passlock you have so you will need to dig around for that since I believe that different passlocks have different procedures. i.e. pass lock 1 and 2. Good luck.