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Just a couple weeks ago, I took my 2012 Dodge Avenger to the shop for (among other things) an oil change. However, the car is already alerting me that it needs an oil change barely 1,000 miles later. Normally the car can go for over 5,000 miles before the oil change alert comes up. So, I'm pretty confused as to what exactly is happening here.

From different sources, I've heard conflicting information about how modern vehicles generally judge when it's time for an oil change. Some have said it's a simple mileage calculation, which can be reset by certain procedures after the maintenance has been done. Others have claimed there are sensors which actually measure the quality of the oil to more appropriately determine when a change is really needed.

Depending on how the alert is being generated, I'm figuring one of a few things is happening:

  1. The computer alerts to needing an oil change based on a certain elapsed time, mileage, or other constant metric. This should simply mean that the mechanic at the shop forgot to reset the counter. I'm really hoping this is all it is, as the alternatives aren't all that great.

  2. The car has sensors which measure physical properties of the oil and alerts to needing an oil change when the oil quality falls below a certain threshold. I figure this branches off into one of two possibilities - both of which I'd file under Bad Things.

    • The mechanic put bad or contaminated oil into the car. Either the wrong grade of oil was used, some old oil was reused, or whatever oil was used had serious quality issues to begin with.

    • The engine is having serious problems which is causing the oil to prematurely degrade. I'm really hoping this is not the case.

So, which method is the Avenger using to determine when an oil change is needed?

Year/Make/Model/Trim: 2012 Dodge Avenger SXT
Engine: 2.4L I4
Transmission: 6 speed automatic

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There are two different types of oil life indicators, as discussed on this page.

First, there is the Algorithm-based one:

Algorithm-based oil indicators measure lots of factors and then plug the resulting numbers into a formula. Based on the answer to this complex, ongoing math problem, the indicator display will tell you whether the oil is OK, is close to requiring replacement or needs replacing immediately.

The other type is the the direct measurement type:

Direct measurement oil life indicators measure the condition of the oil -- the opposite approach to the system described above. This method uses sensors to sample the oil and determine its remaining life based on any of the following:

Conductivity -- how easily electric current passes through the oil (typically, the lower the electrical resistance, the more contaminants are in the oil)

Mechanical properties -- piezoelectric sensors can tell how thick the oil is by the force feedback it gives when sloshing around

Soot concentration -- dirty oil's days are definitely numbered

Presence of water -- water is an impurity in oil, since it hampers the oil's effectiveness and can corrode metal surfaces

I found sources which say the way Chrysler detects for oil change is the same way as GM does it, which is the first method, starting in 2012, so would assume it was using the second method up to that point (which may be a bad assumption). I don't know what to tell you as to why it might have popped early, but it may be due to some type of contaminant, at least that seems most likely.

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I went ahead and pulled out the manual for the car last night. It said something to the effect of the measurement being usage-based (i.e.: things like odometer/number of engine revolutions/etc, which do not directly reflect the quality of the oil, are used instead of an actual testing of the oil itself).

It did not specifically say the odometer was used, but it did state that mileage between changes may vary based on usage. It also includes instructions for resetting the counter(s) for the oil change metrics.

  1. Turn the key to the key-on, engine-off position.
  2. Fully press and release the gas pedal three times within ten seconds.
  3. Turn the key off.
  4. Start the car and check the system status to verify reset.

I'll update this with direct quotes from the manual later.

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The oil indicator is based on an algorithm, monitor(a piece of software). The ECU clock has ticks. When the engine has been operated to a number of ticks(time) the oil light is illuminated. The number of ticks is added to by the average oil temperature and the number of combustion events. Combustion events expose a small amount of oil to degradation by acids, unburnt fuel and other by-products which leak past the engines piston rings. Once the prescribed number of ticks has been arrived at the oil light comes on. The system is a very good indicator of oil condition, but of cause is not of absolute precision.

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