I had a very similar issue with an Impala.
Tried everything...new BCM, both parts of ignition switch, bypass method found on the web...
You know what it was? Very light rust/corrosion on fuse/breaker prongs.
Cleaned it off the light sandpaper and never had another problem.
Still have the car w/250,000 miles on it now.
Try that 1st.
Good luck.

 

Can someone tell me where to look for this?

2003 Pace car is having the same issue..

GM dealer said just yesterday. if the security light comes on again you may have to replace passlock?

They scanned the car. reset the BCM and PCM. said no codes. And oh yeah. We love your car. But $101 will get you on your way.

The car started fine. No lights. Get home, shut car off. 2 hours later NO START.
I called dealer back 3 times for advice. Service manager said to try the 10min on, off, 10min on, off, 10min on, and start.
First time I screwed up. Had to start over.

If this rust near the fuse breaker prongs will get rid of this?? PLEASE TELL ME WHERE TO LOOK?

MUCH, MUCH APPRECIATION.
I don't have the $400 plus dollars for a new passlock system.

 

Well....... the driver door trick actually worked for me.

Locked the door, closed it, had to use key to unlock due to the power locks being disabled.
But. The car started on the first try. And 4 more tries after this.

A major improvement over yesterday. I had to winch the car back in to my barn because it was not starting.

Now the Security light is on constant. Yesterday it flashed between Battery/Security/Service Car Soon.

But I'd still like more info on this rust on the fuse condition.

 

Sorry I wasn't clear..it was the fuse to the BCM.
On the Impala, seems like it was on the driver side panel, but don't remember which fuse.
It was very light oxidation, not really rust.

Here is a vid I posted on YouTube when I was having the trouble.
You can see and hear exactly the trouble I was having.
Be sure & carefully read the info and all the comments, they may help.
I still receive at least one or two comments or emails a month concerning this video and/or the problem. Amazing.
Again, Good luck!

 

Thanks for the info and link.