security light, 2001 chevrolet 3500

well it just started a coupleof weeks ago that blinking security light  going off and on just when my warrenty just expired .well to make things worse now when you turnthe key to start it cranks turns on for a second then turns off any ideas before i tow this truck to the dealership and pay a arm and leg to find out whts wrong ?

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yogibear2007

Is there a remote start installed in it?

The probable cause is the sensors for the Passlock II located in the key cylinder. The contacts inside wear out causing the problem you are describing. The dealership will probably replace the key cylinder and then reprogram the car's BCM to work with the new cylinder.

If you could get the truck to start, it would be possible to override the Passlock II system by cutting the yellow Passlock wire leading up to the key cylinder. You have to do this when the truck is running. The security light would then come on solid every time after starting, but you would be able to start it.

You can also try leaving the key in the ON position for at least 20 minutes to reset the Passlock II. The security light will flash for a while. After about 15 minutes or so it should turn solid, and then go out (if I remember correctly). Then try to start the truck. If this doesn't work...call the tow truck.

Is cutting the wire on the Passlock system while engine running going to disable the system permanently or just on that ignition cycle? It was my understanding that the system would check for the correct "code" each time upon cranking.

I believe cutting the yellow passlock wire will put the system in failsafe mode which wil allow it to start after that point. Someone else here should be able to confirm.