Re: Service Vehicle Soon light
Maybe you didn't see this in the first thread you posted in so here it is again.
The Haynes manual won't give much information on the BCM as it's not user serviceable. Sure you can take it out and put a new one in but then, unless you have access to a factory scan tool, you won't be able to set it up and program it. Theft deterrent has to be relearned, the vehicle option content has to be set correctly. For that kind of stuff it's off to a dealer or properly equipped independent facility.
For anyone that reads this in the future, your DIY retailers, Pep Boys, AutoZone, Advance Auto Parts, most likely have limited access to codes. If the check engine light is on, they should be able to give you a code, with BCM, ABS, HVAC and other systems, probably not. Codes are normally stored until either the battery is disconnected or a given number of ignition cycles occur, in GM's case, usually 40 key cycles. When going to an independent facility, make sure you ask if they're equipped to scan all the vehicles modules for codes. Most won't be able to do them all but the ones that made the investment to do so, will have most everything a dealer scan tool will have.
Again for those that read this thread in the future, the ignition switch on the '97 to '05 malibu, just gen 5 malibu now, had a good deal of issues with voltage dropping out and causing all sorts of issues. The BCM's were not nearly the trouble that the ignition switches were. That said, the BCM is the Power Mode Master and it's job is to wake up the modules at key on. The BCM can fail, and fail in numerous ways, and be intermittent as well. Just a little info so you get some sort of feel for what a service advisor MAY say to you. If you make a post in the future and have already had the vehicle to a service facility, any codes that were set should be in the text of your post to make diagnosis assistance easier.