Hello,I will be glad to try and assist you with this,Welcome to Just Answer.
When you try to start this when this failure happens does the starter engage at all or a click or anything?
Does your ignition key have the little black chip in it that is visible on the key?
Let me know,Thanks Pete.
o.k,this vehicle doesn't have the older style security system then,also you have had all the components checked or replaced that are involved with starting of this vehicle except the electronic ignition switch.
This switch can fail commonly on these GM model vehicles as we have had to replace several of these before for this concern.The electronic ignition switch powers up multiple components when turned on and also powers up the crank/starter fuse,relay and then sends the signal to the starter to engage the starter to crank over and start the engine.
Since it will intermittently start we can assume the security system is o.k. on this vehicle as well.This pretty much leaves us with a possible internal electrical failure within the electronic ignition switch.
Sometimes you can do a tap test on these switches to see if the vehicle will crank and start then.If you can remove the plastic steering column cover under the ignition cylinder you will see this switch,then while trying to crank the engine over to fire up tap on this electronic ignition switch and see if the starter engages and the vehicle starts.
If it does then we know that the ignition switch is faulty and needs replaced.
Also another test you can do is if this vehicle has a starter or crank fuse use a test light to test this fuse for power when cranking,if no power is on the fuse when cranking then we can assume the ignition switch is faulty and needs replaced.Very common on these vehicles.
This could be what is failing on your vehicle here.
oops,yes didn't see the year,the ignition switch will either be located behind the cylinder on the dash or just below it but it is connected directly to the ignition cylinder so you cant miss it.
o.k,in most vehicles the light should have lit up,this voltage signal usually comes from the ignition switch.We know the ignition switch is ok because it has been replaced.You could double check the wiring connections from the ignition switch to this breaker or fuse box and make sure it is o.k.
If it is o.k. then you could have a security issue here,this would have to be checked with a scan tool to see what code(s) are setting and may aid or pinpoint the failure.
It could be possible that the ring has failed around the cylinder and may be intermittently not receiving or sending the right signal to engage the starter,but I would have fault codes checked into first.
yes the scan tool can be plugged in with the ignition key switched on,then the codes can be checked and read out to see what codes if any have set.It could very well pinpoint the failure.
Keep in mind though you will need a scan tool that can read codes from the body control module and the engine computer,some cheaper scan tools will only read codes from the engine computer.
I hope this helped in some way,Thanks Pete!