1998 Isuzu Trooper odometer/tripmeter

Are you saying that the return trip shows less miles that the trip out there?

I saying going the same route that is 177 miles the vehicle says it is 166 miles both ways

I don't know how you can be so sure that the 177 figure is correct. If you are relying on street signs or maps, you have no idea what points they were measured from.

Just because a sign says it's "X" number of miles to a city, you don't know where in the city that measurement was taken or when.

if you go back to my original post. my 177 mile figure! as by the odometer/trip meter I reset it every trip.. now my trip meter says its 166 miles. now any mechanical reason why my vehicle is doing this

I suppose the speedo could go out of calibration but I have never seen it happen.

I know you said nothing mechanical has been changed but also make sure no program updates were done to the computer either. The speedo calibration can be altered that way also.