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The OLM does NOT just monitor engine revolutions. Each specific engine has a stored maximum "bank" of set engine duty cycles (revolutions) between OCIs, reset by the user at time of service. Each time the PCM fires, it subtracts the number of revolutions from the bank. When the bank = 0, the "Change Engine Oil" or oil light illuminates. Outside air temp, coolant temp, cold soak time, throttle load, vehicle speed, etc. are all accounted for in an effort to predict oil temperature, which in turn assess an exponential penalty factor. If the oil temp is above or below the standard algorithm allowance, the amount of degradation increases and is subtracted from the bank value at a higher rate. Hence, if you drive short trips in cold temps, the OLM ticks away faster. If you track your Vette with high rpm/loads, the OLM ticks away faster. If you tow, well you get the idea...
The ONLY thing the OLM cannot account for is a mechanical engine fault. If you have a leaky air filter or a coolant leak, the OLM will never know or change it's signaled OCI. This is where and oil condition monitor would be superior. GM chose this route for simplicity/cost. They are willing to stake a 5yr/100K powertrain warranty on it, so it can't be too terrible.
IMHO, the intervals are a bit on the high side, usually signaling for a change right at the time the oil is spent. I prefer a buffer of 10-20%, but have no qualms about going to 0%. I have yet to see a bad UOA by following the OLM