SOURCE: 99 GMC Sierra Pickup: Crank but no start. starts
The theft light issue is a good observation. Have you replaced the key tumbler or an ignition component lately? Has there been a lightning storm close very recently?
What the flashing security light is indicating is an attempt to relearn the key you are using.
Turn the key to run position, allow light to flash for 10 minutes, when light stops flashing turn ignition to OFF position for 5 seconds, turn ignition to run position and start over. Do this for 3 consecutive cycles, the the theft system will relearn the key cylinder code and store it once again.
Try that first before you go any further.
Let me know what you find.
Regards,
SOURCE: 2001 chevy silverado 1500 headlights wont shut off
You will have to have the dealer reset the security light to restart vehicle.Check all engine and chassie grounds because this is where the lighting would exit the vehicle.It sounds like a ground burnt through.
SOURCE: replaced the fuel pump in 2001 yukon xl. Cannot
CHECK FUEL PUMP FUSE AND RELAY.ALSO SCAN VECHICLE TO CHECK FOR PCM PROBLEMS.
SOURCE: 2001 Yukon Denali: The security light came on my 1999 Yukon Denali ye...
The security system (Passlock) is having problems, it's typical on those trucks. You can find a great write-up here: http://newrockies.ca , it was the only thing that saved my Park Avenue.
SOURCE: 2003 alero security light flashing and won't start
The security light is a visual indication that something in the car's antitheft system is failing. In most GM cars and trucks there is a hidden system that most people are unaware even exists. From the moment you put your key in the ignition, there begins a constant line of communication between your key's security chip or transponder, to the ignition's lock cylinder, and then to the car's TDM. (Theft Deterrent Module) The TDM is what tells your computer that the correct key is being used and that it is "OK" to allow the vehicle to start and run. These 3 parts must be in CONSTANT communication. If the key is in the ignition, then these parts are sending important signals to each other. The security light illuminates when that signal gets broken, even just for a second. When the signal breaks, (normally due to a failing/broken part) the car goes into antitheft mode. The car misinterperates this and thinks its being stolen or hotwired because it is NOT getting that signal from YOUR specific key. There is where the security light turns on and shuts down your vehicle. So basically, if that light is on, your system has some sort of failing part. This can start as an intermittent "no start", to your vehicle not running for days at a time, to the vehicle NEVER starting again. The problem is electrical and computer based, so don't count on an easy reset button, or the problem fixing itself. The hard part is isolating which part is the problem. You can spend a thousand dollars through a mechanic very easily. I have had great luck with bypassing the entire system. This way the problem will never return. It actually CAN'T ever return and can be done yourself at a much cheaper cost. Read through this link very carefully. You'll find alot of information and pictures, along with ways to help you fix this.
http://vatspasslockpasskeysecurityhelp.yolasite.com/
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