The GM OLM PID *is* accessible with Alex Peper's OBD2 Vehicle Explorer and does exist on the 2004 Chevrolet Malibu Classic.
When I checked it today, it was at 0.5% oil life remaining, which apparently really means 0% oil life remaining.
I'd considered the problem of how to reset it. Because this car doesn't "officially" have the GM OLM, no provision had been made to reset it: The button to push in the fusebox wasn't there, the trip odometer didn't support anything having to do with the OLM...using the radio to reset it like some GM cars do? Forget it, the base-model radio isn't that sophisticated and even if it were the uplevel radio it probably still couldn't do it.
So I used Google to search for "GM OLM RESET" and found, in an article on
http://www.gmtechlink.com a method that GM suggests for some models:
Turn the ignition to on without starting the engine, then push the accelerator pedal to the floor 3 times within 5 seconds.
I reasoned that this would most likely work, as the accelerator pedal is connected directly to the PCM wherin resides the GM OLM software and all of the other methods seem to go through the body control module first.
So I tried it. It took a couple of tries, apparently if you go too fast it won't register and won't reset the OLM. Or maybe it needs more than 3 times..either way, I got it to reset by pushing the gas pedal to the floor several times.
When it did reset the OLM, it went to 100.5% oil life remaining. I have no idea why it always adds .5% to the oil life remaining.
I'm going to check it again in a couple of weeks and see how much it's dropped. That'll give me an idea of just how severe my mom's driving really is.