Have a 2013 Highlander. Since the GPS in the car is pretty much worthless, I still use my trusty Garmin that previously was in my 2006 RAV4 and other vehicles. However, the Garmin is showing that the speedometer is off about 2 1/2 MPH. Dealer, of course, says that GPS not accurate and that the Toyo speedometer is within tolerance at + or - 4 MPH. I say that’s crapola (can I say that?) and this GPS along with every other GPS I’ve used in every one of my cars is within 1/2 MPH at most of the speedometer reading. Should I appeal to a higher authority at Toyota?
Um…if the speedo is accurate to within +/- 4mph and the GPS and speedo are showing 2-1/2mph difference, how does he know the GPS isn’t accurate? Sounds to me like everything is within tolerances.
While it seems odd to us, a 2-1/2 mph error is normal. One thing that might help if you have an analog needle it to determine if the error is constant throughout the speed range. I determined on mine that the speedo was consistently 2mph high. So I removed the instrument cluster, removed the needle, and adjusted it by 2mph.
If you have an old-fashioned needle and would like to try this, post back and I’ll see if I can help you figure out how to do so on your car. But if you’re uncomfortable with the idea, just know that 2-1/2 mph is normal. I even have the instrument cluster specs for my car, and I believe mine is +/- 4mph too.
I’d guess a GPS is more accurate than a speedometer. Do you have a long straight highway with mileage markers posted every mile? If so, that’s how I’d test it. If you are driving 60 mph you should pass those marker once a minute. I think an error of 2.5 mph is probably with speedometer specs. And it might not be the speedometer, it could be the tires.
Both systems use an algorithm program to determine the speed of the vehicle. So one might be slightly off from the other.
Did you know tire pressure will effect the difference in reading from the vehicle and the GPS?
Tester
2.5 mph is nothing. The best thing is you know it so you know the speed you are actually going. Mine was off about 2 mph so I moved the needle. Bottom line is you have no real complaint about 2.5 mph, and the dealer won’t do anything.
Sounds like everything s OK. GPS is relatively accurate for speed. It’s impossible to be absolutely accurate like it’s impossible for most to keep your car going the same speed for any length of time. But GPS, like your car speedo is plenty accurate enough. Rate equals distance divided by time so getting an instantaneous rate that’s accurate under these conditions, is near impossible as even that is theoretically the average slope of a line between two points at two different times that are constantly changing. Since the mph as determined by your car is done internally and the accuracy will be subjected to variations in tire pressure and tread depth wear, how can you expect that as well to be absolutely accurate ? It’s the nature of the beast. Be happy it’s this close. Regardless, at some point, when conditions are perfect and match the settings used for factory set speedo, it WILL be accurate. But you won’t know when that happens.
Heck, even the amount that it (speedo) is inaccurate can vary with conditions and speed.