Welcome to TRS
Battery voltage?
Test it, needs to be above 12.4volts or THEFT system will trigger on start up
Turn the key ON, do not try to start engine
Watch the THEFT light, if it comes on and then goes off the fuel pump should run for 2 seconds, but 2 seconds only
Repeat key off and key on 3 more times, that should give you 30-40psi fuel pressure at the rail
Try to start engine
If THEFT light flashes rapidly with key on then you have an issue with PATS
Low voltage as said is most common
If you leave the key on with THEFT light flashing and wait 45-60 seconds the THEFT light will start to flash a 2 digit code, 11-16
These are what the codes mean
11 Transceiver [transponder coil] not connected, or there is no power to it.
12 Transceiver internal fault.
13 No Key/no PATS key has been used to turn the ignition switch.
14 Incomplete key code received.
15 Invalid key code received.
16 CAN communications error.
Just a heads up, if you trigger the PATS system, "flashing THEFT light", 4 times then PATS will go into LOCK DOWN, it thinks a theft is "in progress"
You have to wait 90min to 2 hours before it will reset
Unhooking the battery doesn't help to shorten the time in fact it would make it longer as the 90min timer restarts when battery is hooked up again, lol