Maint Reqd Light Does Not Match Engine Oil on Info Screen, Why?

[CBarr31]

Ok, first a brief history for everyone that doesn't know this. Under the "Info" button to the left of your MFD there is a "Maintenance" screen where you can set miles or dates for additional friendly reminders to perform regular PM's.

Ok, with that being said I set the "Engine Oil" at 5000 to remind me of my oil changes. Of course as everyone knows at 5000 miles the Maint Reqd light on the dash also comes on steady. It begins flashing at 4,500 miles to let you know you are approaching 5,000 and comes on steady at 5,000.

That being known I noticed the last few times that my Maint Reqd light came on substantially earlier than my "Engine Oil" mileage reached zero. I actually pulled over and checked the difference immediately when the Maint Reqd light came on this time and the difference was 96 miles!!! How is that possible?

The first theory everyone will say is that when Toyota changes the oil they reset the Maint Reqd light and then "test ride" the car. There are 2 problems with that .... 1. a 96 miles "test ride" would take a couple hours, LOL 2. I use Toyota high speed service so the car comes from the oil change to me within 50 feet and is NEVER out of my sight. When I get it I reset the "Engine Oil" maintenance item immediately before leaving the dealership.

The second theory everyone will put forth is that changing my tires to Michelin Harmony 195/60 R15's has "altered" my true ODO reading. There are also 2 problems with that .... 1. The ODO matches mileage markers on various interstates that I have checked it with. Granted these sometimes are not precise but then again the ODO can only read in tenths anyway. So unless I put it on the Dyno at the shop this is as close as I feel like getting. 2. The ODO EXACTLY matches the mileage in the "Consumption" screen on the MFD. This seems more relevant to me because I assume this number is what is used to countdown the miles under "Engine Oil" in the Info screen also on the MFD.

Soooo, all you "Techs" and "Gurus" out there can someone explain to me why these two numbers don't match? I would accept a slight difference of 5, 10 or even 20 miles occasionaly but a 96 mile difference is HUGE.

Looking forward to the responses to this post. Talk to you soon and Happy Driving!!!

Chris

[CBarr31]

3 days and 103 viewings later no one has any ideas? That's kind of a bummer, LOL. I'm still hoping for someone to have "eureka" moment but don't expect it.

Chris

[Mjolinor]

Distance travelled and needing an oil change are not as closely related in the Prius as they are in other cars. Maybe it is deliberate on Toyota's part and your engine has been working harder this time than on previous occasions.

[bedrock8x]

Let me give it a guess.

The ODO and speedometer are set to 3-5% higher than actual. Scangauge can verify this. It is known the calculated mileage is 1-3mpg lower than the MFD.

I suspect the Maintenance Require uses the ODO reading and the reminder function uses the "real" mileage from the CAN bus, so the later is legging behind.

[CBarr31]

Bedrock8x,

That is as good of an explanation as I think we are going to get without actually looking at the code or having Toyota answer the question for us.

It just makes you wonder why they would write the code that way and use two different mileages like that knowing that it would cause this kind of discrepency. Maybe this was corrected in the 3G, LOL. Nah, I doubt this was at the top of Toyota's list of improvements .

Thanks for the response and theory. Until proven otherwise I declare you the all knowing winner of this little trivia challenge.

Happy driving!!!

Chris