security light on
Last time this happened to me I had put in a remote start button so I could at least crank the motor. This time it would crank with the remote button and start but not stay running until I messed around with the key a bit. Now it'* fine again. I'm thinking it must be something to do with the resistor in key system. Bad connection.

you can bypass the resistor in the key with a same value resistor in the line that goes under the dash that will bypass the key part, but there is more to the system, i would start there though. if you have cleaned the key terminals with some alcohol or tried another

Here is a good link to help with the resistor trick.

https://www.gmforum.com/electrical-1...2-99-a-279119/

Thanks for your replies. That'* a great link on how to do it.

Very welcome, I also have a link with a little more detailed info and pics, a lot of the info there is exactly the same as what you got in the first link, there are a few good pics that are helpful though.
How to bypass the VATS system in a late model GM vehicle

That one'* even better. Thanks.

You're welcome, and good luck, let us know how it goes.

I recently had a similar issue with the Anti-theft (GM should have called it "Anti-start") system in my mom'* '99 Intrigue. I have found a fairly successful way of working around this system with a recalibration of the ignition sensor.

I made a fresh copy of the original key (which was in good condition due to non-use, but I've seen copies of worn keys work better than the worn-out originals)... Then, I disconnected the battery for 30 minutes, inserted the original key in the ignition, reconnected the battery, and turned the key to the "Run" position (don't attempt to start it) for 20-30 minutes. Then, I turned the key off, turned it back on, and started the car, and the Security light has not come on in three months.

My mother has been using the copy I made of the original since that day, and the ignition was calibrated to the original. Your experience may vary. The procedure for your car may also be different. It has completely eliminated having to bypass the VATS system, and it'* a really inexpensive thing to try if you have an hour to kill.

Good luck, and let us know how it turns out!

It sounds like your Moms car has passkey 3, and did not have the resistor pellet in the key, because similar instructions are posted via the same site that has the VATS bypass.
How to start your late model GM vehicle with a flashing SECURITY or THEFT SYSTEM light

I don't think that security relearn way is going to work for them, but it may help somebody that actually has PK3.

Oh yeah. *smacks self in forehead* I forgot they went through several iterations of Passkey/VATS... Yes, you're right, my mother has P(ain-in-the)assKey 3. I didn't stop to think about the different versions...

I didn't see any vehicle info, so I just kinda blindly posted without making sure I had the right system. Oops!