2011 Chevy Impala 3.5 Security Light on No Crank No Start

2011 Impala LT 3.5. recently had a problem similar to now with the security light staying on and not allowing to crank. let me start off by saying that I'm not just some DIYer I'm an automotive technician and currently I'm the diagnostic technician at the shop I work at in Sacramento CA. but this one has me needing some help probably cuz it's my own car and there for more stressful but none the less I recently just had my vehicle theft deterrent module go out on me it's the part that goes around the ignition lock cylinder and who's job is to read the chip in the key.. well not a big deal just replaced it and did the relearn for the key car fired right up and hasn't had any issues til now. except now when I turn the key to run jus like last time the security light stays on except this time there's no message on the instrument panel saying service theft deterrent or anything at all regarding the security light being on. scanned car and it didn't even have communication with the theft deterrent module now it just makes it even harder because the last time I fixed the security light issue I didn't have a scan tool with me so idk if I do in fact am supposed to be able to communicate with a theft deterrent module or not but I currently have no codes in the BCM and only 1 code in PCM for oil pressure sensor circuit high. The only thing I got any feedback from regarding the security light was from the IPC or instrument panel which gave a U0168-00 code which is for no communication with vehicle security module.. thts it. I've tried doing the relearn again except I can see under live data tht the relearn is not starting and is inactive and I can't get it to start to relearn no matter how long I let the key sit in run position or whether I attempt to crank the car or not it never starts the relearn and I never get any message in the instrument panel saying anything about needing to service theft deterrent or anything about the security light it's simply just on and there and won't let me crank the car. pls can someone help me out here on where to look

Without communication to the antitheft module you can't program keys obviously nor will the car start, as you already experienced.

You have to have communication back in the first place. Loss of com is possible due to a variety of reasons as wiring issues, defective module....

A good start is a wiring diagram and SI to educate yourself on normal system operation and go from there.

If you still have the old module/antenna you may want to plug it in just to see if you get com back. If so you would know the new module is at fault.

ok I guess it was jus more obvious the first time that the theft deterrent module was bad due to the fact that on the motherboard of the module it was scalding hot so obviously something was wrong but this time there was nothing like that

You might want to check powers and grounds and fuses if you haven't already. Then see if you have undesired voltage on other wires going to that module. As well as see if the connector was fully seated which if it came out could be your issue. But if this module is cooked then chase those wires for problems before hooking another one up.

Another thing to look at would be any aftermarket car alarm/remote start or radio wiring and make sure it was connected properly and not to data wires etc. Especially to anti theft module.

Hey did you ever figure this out? Im having the same issue with the same car