A faulty (Bad PCB) Chinese knock off Tech 2 scanner got connected to my '03 SS and wreaked Havoc on the electrical system. At that moment all dash lights and gauges went crazy and speakers started buzzing. Immediately disconnected and all was normal except the battery was drained. Recharged and all seemed fine. Car sat for a few weeks and the battery drained a few more times while sitting, again recharge resolved problem. Last weekend I replaced the transmission and went to start up for test and got a flashing Security light alternating with a battery symbol. Went to crank and got the click, click, click of the starter drive gear engaging the ring gear , but would not crank the engine over. Sounds like a dead battery, but tested at 12.6 volts. Swapped battery, same problem. Tried Passlock relearn-no luck. Checked all grounds, fusible link, swapped starter, checked starter connections, fuses and relays. Connected my real Tech 2 and got no current DTC's but several in history including some "U" (PCM) and "B" (BCM etc...) codes probably from the event. PCM seems OK because I have a check engine light and can communicate with it though the Tech 2. I'm thinking either the BCM is fried or it's a Passlock issue.
Sorry for the long post, but I think details are necessary here.
I'm no wizard with auto electric, so all opinions and advice are welcome.

 

Mine had a lot of the same issues, and a new bcm solved the problem. h

 

Thanks for your reply Hemivette.
I considered the BCM, but I have checked the BCM with my Tech 2 and there are no current DTC's, only ones stored in history and according to the book, if there no current DTC's the BCM is OK.
I'm leaning toward a bad ignition switch and bad passlock module in the ignition cylinder.
Did your car "click, click,click" when you tried to start?
I'm also hearing an unusual "clicking from the glove box area.

 

Actually mine would start and run one day, then have a dead battery (or symptoms of one) but was never really dead. I think it seems like its dead cause these cars have circuit that cuts off the battery when is senses a draw type issue. Mine did the same thing with the lights and relays going nuts, and when it would stop the battery would act like it was dead, but if I disconnected it for ten min or so, and hook it back up it would be almost a full charge. I even went as far as buying a new batt., and nothing changed til I bought the new bcm. I even put the original batt. back in, and all is good. h

 

I've also bought a new BCM, but have been hesitant to replace it since reading the comment in the book about it. Put my hands on the connectors to see how they unplug buts it's pretty awkward under there being 6'4", 300 lbs. Lol.
Didn't want to break something. What is the trick to disconnecting the connectors?

 

I'm right up there with you at 6, and 265. I was able to reach up, and grab the bcm with one hand, and use a screwdriver to unplug it with the other. It has to be unplugged to come out. h

 

But what's the trick to releasing the clips for the connectors?

 

If you look at the new one you can see where they unclip in the center of the plug. I used a small L shaped screwdriver to lift up, and out, while pulling on the harness. h

 

Sorry for the late update, but I found the problem to be a mis-landed ground wire. In the process of installing the new transmission I connected a ground cable to the starter instead of the stud bolt connecting the engine to the transmission where it was supposed to be. This prevented the circuit of the the theft deterrent system from being completed. After correction and a security re-learn procedure problem was solved.

 

That's one of the things in tinkering with on my car at the moment is cleaning up and up grading all the ground connections. good solid grounds make a happy car,