Here is a rather long read from someone who helped develop the original Oil Life Monitors for GM (Cadillac Northstar engine)...it may help answer some questions or discussion here...
......... and from the article written by our CF member who was a GM Northstar System powertrain engineer - the early OLM, so adjust your criticisms accordingly - long read -
How Often Should I Change My Oil? The GM Oil Life System:
Q: How does the GM Oil Life System (OLS) work?
A: Vehicle maintenance intervals of three months or 3,000 miles no longer apply to vehicles equipped with this system.Instead of an actual oil-condition sensor, the GM Oil Life System relies on a computer-based software algorithm that continuously monitors engine-operating conditions and driver use to determine when an oil change is necessary.GM has calibrated the system for a variety of vehicles based on millions of test miles over a period of years.The system is now installed on more than 20 million GM vehicles.
Q: How do I operate the system?
A: The GM Oil Life System is very easy to use.Refer to your Owner’s Manual for a description of your specific vehicle’s change oil light or message and instructions for resetting the system.When the algorithm determines that your vehicle needs maintenance,the change oil light or message will illuminate on the instrument panel or the driver information center at start-up.You should have your vehicle’s oil changed within 600 miles of the odometer reading at the time the change oil light or message first illuminates. Immediately after the oil change, reset the system according to instructions in your Owner’s Manual. After the reset,the change oil light or message will no longer illuminate at engine start-up until the oil needs to be changed again.
Q: How many miles can I expect to go between oil changes when using this system?
A: It will vary.The beauty of the GM Oil Life System is that it automatically adjusts the oil-change interval based upon engine characteristics, your driving habits, and the climate in which you have been operating your vehicle. For instance, mild highway driving in a warm climate will maximize the interval between required oil changes. Depending on the vehicle,this could be as high as 12,000 miles.On the other hand, short-trip driving in a cold climate may limit the interval between oil changes to 3,000 miles or less. In general, most people who combine city and highway driving find that the GM Oil Life System will indicate the vehicle needs an oil change every 5,000 to 6,000 miles.Most people maintain consistent driving habits.This means their mileage between required oil changes will be consistent.
Q: What happens if I change the oil and forget to reset the system?
A: Since the GM Oil Life System does not actually sense oil condition, it is important that the engine computer knows when your vehicle has had an oil change.It registers this information through the reset operation described inyour Owner’s Manual.The change oil light or message will illuminate at start-up until the system is reset.The more miles you drive without resetting the system,the more inaccurate the GM Oil Life System will be.If you drive more than 500 miles after an oil change without resetting the GM Oil Life System,you should default your oil-change interval back to 3,000 miles.After you change the oil and reset the system, you may resume normal use of the system.
Q: I change my oil every 3,000 miles.How does this system help me?
A: You may continue to change your oil every 3,000 miles if you choose, but the GM Oil Life System allows you to extend your mileage between changes without harming your engine. It takes the guesswork out of your vehicle maintenance needs,calculates when you need maintenance, and it provides efficiency and convenience.It also is an economically sound practice that protects the environment by minimizing the amount of oil used and discarded. Remember, however, to reset the system after the oil change or you will get a false reading from your change oil light or message.
Q: Do I have to use special oil?
A: The GM Oil Life System calibrates your needs based on the use of standard factory-fill automotive engine oil that displays the “Starburst”API® Certification Mark. This verifies that the American Petroleum Institute certifies it for use in gasoline engines.Make sure to read your Owner’s Manual to select oil with the viscosity and grade that is correct for your engine. Any oil you use should carry the API “Starburst”mark. The Corvette and a few other GM vehicles (2004 CTS/STS/SRX) are the only ones that require synthetic oil.
Q: The oil-change service station recommends that I change the oil every 3,000 miles. Why should I not believe them?
A: The 3,000-mile oil change is a very conservative approach to maintaining your vehicle that dates back to 1968. Since then, there has been many advances in both engine design and oil technology. These advancements, in conjunction with the GM Oil Life System, allow you to increase engine oil-change intervals without risking harm to the engine.
Q: I change my own oil. Should I reset the system myself?A: You may reset the system according to the instructions in your Owner’s Manual, or you may ask your selling dealer for assistance.
Q: Will I damage the vehicle if I don't change the oil soon after the change oil light or message comes on?
A: As your Owner’s Manual specifies, you should change the oil as soon as possible after you see this indicator.We recommend that you change it no more than 600 miles after the message first appears.
Q: Do I have to check my oil level now that my vehicle is equipped with the GM Oil Life System?
A: Yes, because the system does not sense oil level.As your Owner’s Manual specifies, we recommend that you check your oil every time you stop for gasoline.
Q: Will I void my warranty if I don't follow the GM Oil Life System regimen?
A: To maintain your warranty, you must comply with your Owner’s Manual recommendations. We suggest you read it.
Q: I had my vehicle’s oil changed recently but my GM Oil Life System indicator is still on.Why?
A: If the light is still on,the system may not have been reset when you changed your oil.You may reset it within 500 miles of your last oil change. If your vehicle has exceeded this mileage, change the oil at 3,000 miles and then reset the system.
Q: I still prefer to have my oil changed at about 3,500 miles.What should I do?
A: It is OK to change your oil before your vehicle notifies you that you are due for an oil change. Be sure, however, to reset the system when you change the oil, even if the GM Oil Life System light/message has not illuminated.
Q: I have driven 6,000 miles since my last oil change.My change oil light/message has not come on, but my oil seems dirty. Do I have a problem?
A: Your vehicle’s oil may discolor under normal conditions, depending on driving conditions. Refer to your Owner’s Manual for additional information.
Q:Can any dealer other than my selling dealer perform Simplified Maintenance?
A: We recommend that you care for your vehicle through your selling dealer so you can build a relationship with the team that sold you your vehicle. However, any GM Goodwrench dealer can perform Simplified Maintenance and reset the GM Oil Life System for you.
Q: During the summer,I drive my vehicle in a very hot climate. Do I need to change the oil more often?
A: The GM Oil Life System calculates your vehicle’s needs based on a wide range of driving conditions, including more stressful situations such as severe climates, trailer towing, or stop-and-go operation.There is no need for you to override the recommendation of the GM Oil Life System.
Q: I continue to get 3,000-mile follow-up mailers from my GM dealer. What should I do?
A: Inform your servicing dealer that you prefer to follow the Simplified Maintenance schedule determined by the GM Oil Life System and would like them to adjust the type of follow-up mailings they send you.
Q: I have a 2002 model GM vehicle with the GM Oil Life System.Can I use the Simplified Maintenance schedule with it?
A: Because Simplified Maintenance was not yet introduced before the 2004 Model Year, continue to use the recommendations in your Owner’s Manual for that vehicle.
