MM and engine air filter
 

How does the MM determine when to indicate the need to replace the engine air filter? Does it do so simply on the basis of mileage, or can it sense when the filter is becoming clogged?

Unlike the MM's Oil algorithm, the air filter is based purely off mileage.

While it could be by the pressure drop across the filter I suspect its by miles. We always shake the filter backwards to remove any loose trapped stuff nothing else. If the filter can't see light thru it we replace.

Thanks--that's what I suspected.

To answer any subsequent questions, the MM doesn't "sense" or test anything for any maintenance item.

It will count statistics from the other live sensors, and then use algorithms based on that for maintenance.

So if you reset the MM, everything goes back to 0. (which if you think about it is why they have a reset, rather then just auto-detecting the state of the item, right?)