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GM Oil Life Monitor — How it Works

How does the GM oil life monitor work?

The oil life monitor doesn’t use a sensor to determine oil condition

People think that the oil life monitor system relies on some type of sensor that detects oil condition. There is no such sensor. Instead, the system tracks your actual driving habits and uses an antilogarithm to determine how your driving affects oil life.

GM Oil Life Monitor was introduced in 2007

The monitoring system was first introduced in 2007. It tracked engine usage and told you to change oil in as little as 4,000 miles if you drive under “severe” conditions or as long as 12,000 miles in optimal conditions. However, the system didn’t tell you how much oil life remained; it only told you when it was time to change your oil.

GM Oil Life Monitoring Changes in 2013

Starting with the 2013 model year, the oil life monitoring system bases the remaining oil life on the factors shown below. The system assumes you’ve used the correct DEXOS oil and that you check the level and top if off when needed. If you don’t check the level and top it off or you fill with a non-DEXOS oil, all bets are off.

What the oil life monitor tracks

After each oil change reset, the GM oil life monitor tracks

• Engine revolutions —The GM oil life monitor starts with a factory preset number of engine revolutions stored in memory. Every time the engine is started and run, the oil life monitor tracks the number of revolutions run and subtracts those from the factory programmed target.

• Engine temperature— The algorithm incorporates multipliers that reduce the number of engine revolutions and thus remaining oil life, based on how far engine oil temperature varies from normal oil temperature. If the PCM records an engine temperature above 260°F, the remaining oil life will immediately show 0% remaining life. Cold starts reduce oil life and the algorithm takes that into account by reducing the number of revolutions accordingly.

• Miles since last reset—The monitor records miles traveled since the last oil reset and maintains a MAXIMUM value of 7,500 miles for ALL 2013 and later GM vehicles (except the Volt) before it show 0% remaining oil life.

Time—The oil life monitor records the amount of time the engine runs since the last oil change reset. The time tracking is a liner measurement and decreases remaining oil life on a straight life basis in conjunction with the other tracked variables. The monitor will show 0% after one year regardless of miles driven, engine revolutions or time run.

When to change oil on a GM vehicle

Regardless of what self-proclaimed experts, oil distributors or oil companies may claim, the maximum oil life on GM vehicles (except for the Volt model) is 7,500 miles or less. Oil life depends on time, miles, temperature and engine revolutions. Do not be fooled into thinking you can go beyond this limit.

Factors that degrade oil and reduce oil life

Oil Oxidation reduces oil life

Oil contains anti-oxidant additives to combat oil breakdown due to oxidation. But as oil meets heat, foam and water, those additives get used up and the oil oxidizes, turning into sludge.

• Idling in slow traffic causes oil oxidation

• Cold starts with a rich fuel mixture causes raw fuel and water to enter the crankcase and mix with the oil, causing oxidation and breakdown.

• Turbochargers operate at very high heat. Driving at highway speeds and then shutting down the engine can oxidize the oil left in the turbo.

• Not checking oil level causes the remaining oil to work harder and use up its antioxidation additives much faster.

Engine overheating will deplete remaining oil life

If the engine coolant temperature exceeds 260°F, the oil life monitor will immediately to to 0% remaining oil life.

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