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When we had the 06 LS 430, its estimated MPG were spot on, compared to hand calculations, and no more than +/- .2 MPG if off.
The LS 460 is consistently off between .8-1.2 MPG. I track my fill-ups on fuelly.com so I'm not relying on the car's estimates but I still wondered why a more advanced LS is so inaccurate compared with the LS 430. Well, it seems the LS 460 is also not accurrately counting miles traveled since the last refuel compared to when I reset the trip meter when getting gas. The is probably why the estimated MPG is so off, due to bad/insufficient data. The estimate is probably correct based on what the LS "sees".
This error may be due to improper "Distance Calibration" of the dead reckoning function of the navigation system. Try doing the "Tire Change" calibration and see if that helps. Refer to your vehicle's Navigation Owners Manual.
This error may be due to improper "Distance Calibration" of the dead reckoning function of the navigation system. Try doing the "Tire Change" calibration and see if that helps. Refer to your vehicle's Navigation Owners Manual.
Thank you, jmcraney. I will give that a try and report back results.
This error may be due to improper "Distance Calibration" of the dead reckoning function of the navigation system. Try doing the "Tire Change" calibration and see if that helps. Refer to your vehicle's Navigation Owners Manual.
jmcraney, it is not clear in the Lexus manual if the car needs to be moving to do the tire change calibration. I would think yes but you can't use the nav, to begin the calibration, when the car is in motion. I tried doing the tire calibration twice, both in park and in drive (while stopped, calibrated, then drove a short distance). Both times, the "calibration" message appears to finish within seconds so I'm not sure if anything got calibrated, especially when not moving. The position calibration already seems to accurately pinpoint where I am.
jmcraney, it is not clear in the Lexus manual if the car needs to be moving to do the tire change calibration. I would think yes but you can't use the nav, to begin the calibration, when the car is in motion. I tried doing the tire calibration twice, both in park and in drive (while stopped, calibrated, then drove a short distance). Both times, the "calibration" message appears to finish within seconds so I'm not sure if anything got calibrated, especially when not moving. The position calibration already seems to accurately pinpoint where I am.
FatherTo1,
I agree with you that the manual is vague about this. There doesn't seem to be any information available, that I can find. I don't have any personal knowledge about it and the only thing that I have to share is my opinion on how I think it works.
The car's Navigation System, unlike smartphone navigation, has a dead-reckoning mode where the car continues to navigate in the absence of the GPS signals. It does this by using the last known GPS position, a heading sensor (the car's magnetic compass) and a distance sensor (probably from counting the driveshaft's rotations). The "distance sensor" is likely calibrated by counting the car's drive shaft rotations and using the GPS to measure the distance traveled - if the GPS samples fast enough relative to the car's speed the car doesn't even need to go in a straight line during calibration.
I am guessing that the MPG calculations are based on the navigation computer's distance sensor and that's why I suggested that you look into that.
I understand your concern about the calibration procedure. It seems confusing, but after some thought I expect it is very simple and mostly automatic. I think that after you start the calibration, by pressing "Tire Change" button, it's automatic and nothing else to do other than driving a minimum distance. The distance is probably something like 1 or 2 or 5 or 10 miles (I would guess it is less than 1 mile) - probably doesn't make any difference if you stop and start or go in a straight line. The drive shaft rotations are counted and distance traveled is computed from GPS fixes and the calibration information is derived from that. I think you just press the button and forget about it.
The other calibration button allows the GPS position bias to be removed (that is usually just a few feet) and the compass error to be removed.
I've expressed my opinion on this before but it is an esoteric subject and no one had any questions or comments.
Please use anything I've said here carefully. And my apologies if I have misled you.
If this doesn't help with your concerns about the distance your car is traveling, I suggest you use your smart phone to check your car's odometer. I believe there are free apps for this.
Last edited by jmcraney; 07-20-17 at 09:12 AM.
Reason: typo correction
Thank you, jmcraney, it seems the tire calibration did the trick. Distance driven is consistently tracked now. Will know soon whether MPG accuracy has also improved (am expecting it to).
07-09-17, 12:49 PM
No wonder car's MPG is so off
