I've been having problems with my alternator and was told that the PCM is bad. The original alternator in the car when I bought it (a month ago) was brand new but still wouldn't charge the battery. I took that one out and installed on from another car that had no electrical issues. I took the original to be tested and it was dead, the voltage regulator was toast. I tested the replacement in the car after I ran it for about 5 minutes (and it didn't produce any voltage) with a CS Generator tester and it tested bad as well. I know it was good going into the car. So I had a new (out of another car) PCM reprogrammed with my VIN number and installed it into the car this weekend along with the rebuilt and retested original alternator. Now I can't get the car to start.

When I turn the key to run, my instrument cluster does the anoalog gauge sweep, displays the previous owners name, and then displays a service brake sytem message (need new pads) then just displays whatever info it is set for (mpg, distance etc) after you acknowledge the service message. The security light is on solid, the red battery icon is on, as is the brake light (from the brake pad DTC) other than that there are no warning messages or weird lights.

When I turn the key to start, the whole cluster goes dark, there is no click on the starter, or the starter enable relay (that i can hear from inside the car) and when I release the key the IP does its initialization all over again. No security system message no nothing. It's almost like I have a very dead battery, but the battery was charged 24 hours previoulsy (although stupidly I did not check the voltage while this was going on) The only DTCs I have is the Brake pad sensor open one (C12xx? I don't remember the whole #) , a lumbar support switch fault (B1845 I think), and a crank variance relearn code (P1336). I'm not familair with how the security system in a 2000+ caddy works, but i would expect it to tell me that there is a theft deterant problem to remove the key and wait 3 minutes like my 97 does.

I should note that the car started just fine on the old PCM. previously although not on this particular day. If I put the old PCM back in, it will smoke my new alternator voltage regulator.

Question is, how does a 2000+ respond when there is an issue with the theft deterrant system, are there any messages shown on the dash panel, any DTCs set?

I'm trying to figure out if I have a PCM issue that needs the dealer to reprogram the keys, or something more simple like i just have a dead battery, although there was enough power to open and close the windows, and the sunroof. I tried to do the 30 minute key relearm procedure but after 10 minutes of the key being in the on position, the security light never turned off so even though the service manual says you can do it, I'm not sure you really can.

If a GM dealer reset the PCM with your car's VIN there should be no problems, but it sounds as if your car has gone into a theft prevention mode.

The red battery icon may be telling you something. Cable/battery connections ?

I'm assuming the red battery icon is on because the car isn't running and the alternator is still grounding the L terminal (or I have less that 10.5V and the DIM is sending the message). Like I said I stupidly didn't check the battery voltage since I had just charged the battery 24 hours before, but it was really dead, took a few minutes for the charger to come up to a descent charge current.

I don't think I have a theft system problem, because I'm not seeing the P1631 DTC - Theft Deterrent Start Enable Signal Not Correct but I don't know what the IP in a 2000 does normally when you have a theft control problem. I can't beleive it does nothing. No "service theft system" message, no "theft system problem car may not restart" message, no "remove key try again in 3 minutes" stuff. It does nothing like that. Literally when I hit the crank position the IP goes completely blank, nothing happens, no attempt to start (didn't hear the fuel pump but then I've never heard it on this car) and when I release it the speedometer and tach do their sweep upscale and the greeting shows up, just like if you put the key to run but didn't start the car, or if you had sucessfully started the car. Radio functions fine, as does the HVAC fan (if i leave the key in on) windows roll up and down sunroof opens and closes (maybe a little slow)