Hi,
Do you have a dongle or tuning device with a copy of the modified tune the EEC’s running ?
Have you verified no spark at the Coil?
EEC failure is rare, more likely wiring, or power supplying it. Do a thorough check of your electrical system.
Check the ground(s) from the battery terminal to your EEC, Chassis, block-leave the.terminal(S) disconnected for an hour or so while carefully searching for and correcting shorted wires, melted wires, substandard or corroded terminations. Pull apart plugs & the covers on all your fuse blocks &
look for water entry, or corrosion, fuses.
Use an ohmmeter and look for any low resistance paths from the positive cable to chassis ground.
Check your battery voltage. Should have 12.5V+ at the terminals, disconnect both terminals & put it on a low charge setting while you’re cleaning & checking things. If voltage is very low, bring it to get load tested. Check your Alternator wiring, and it’s power wire to the battery, corrosion on the plug, etc..
The fact is your EEC is unable to complete it’s self (readiness) check due to self-fault may only be a poor ground, shorted connections, melted wires, pulling the voltage down too low for the EEC to function properly. Has it been running typically of late?
You mentioned the security system (PATS). Was your security light flashing randomly previous to this, or now & how recently did you have the last issue mentioned? If you have another Key, try it. A decent Scantool should be able to see the EEC code thrown from this.
Good luck!
-John