2010 Ford Expedition - Won't start
 

I have a 2010 Ford Expedition which randomly has trouble starting.
When we go to start it the theft light continues to blink and the vehicle won't start.

After awhile we will go back to the vehicle and it will just start like that. What is the best way to troubleshoot this random behaviour. Seems as if it has something to do with the PATS system.
Also happens with both sets of keys but its always random. Will start just fine for a few days and then bam won't start again.

Thanks!

Are there ANY aftermarket devices on the vehicle, like, remote start system, ? Anything that use a Transponder can interfere with starting. Are there any do/dads on the key rings ?
When the light flashes rapidly with a no start , if you wait at least 30 seconds with the key in the run position giving the anti-scan feature time to time out will the vehicle start then?

Nope no aftermarket devices. Remote start but its factory.
No do dads on the key ring other then regular old house keys.
I'm not sure if the light flashes rapidly. The one time it happened to me it didn't seem like it was rapid. It normally happens to my wife while I'm at work so haven't witnessed it to often myself. I've asked her to pay more attention for me.

We will try waiting the 30 seconds and see what it does next time.