It always felt like I was flying when I was driving at 55 mph on the highway. Last night as I passed another vehicle, my speedometer read 55, theirs read 65????? How does something like this happen, and how do I correct it? Thanks.

 

The only thing I can think of, but it would be the opposite, is that you have it switched to kilometers.

 

Does it have 19" rims? Specifically, Whatsizeof tires do you have on it?
I saw in your other post (about it swaying ) that it had the wrong size tires on the front, that will definitely change the speedometer readings.

Try to get some solid data the old fashioned way...make sure your tires are properly inflated,set the cruise control for 60 mph, drive a 3 mile measured stretch of highway, and measure how many seconds it took..it should be 180 seconds

 

mph and kph are not 10 mi off. Something else is wrong, something as simple as the wrong size tires.

 

I would suggest either that most likley tire size is diffrent from stock and is be calculated at a diffrent rate or that your computer is using some wierd axle ratios ect to calculate your speed. did you have a low battery or anything else going on with it? did you have to jump the car?

 

I just bought the car, and the next day the battery was dead, which in fact caused my check engine light to come on and has been on for over a week now!! I don't see how a dead battery could affect my speedometer???? It had smaller front tires when I bought it, but I had the correct tires put on the front, so it now has all 4 factory size tires on it, and it had this problem before???? Its puzzling.

 

CEL will be on due to low battery voltage and can cause communication errors between all the modules. voltages can cause all sorts of wierd problems to happen to modules which is why you might have to relearn one of them in this case.

 

Can I relearn them? And if so, how? My husband unhooked the battery this morning, and then re hooked it and for now the CEL light is off????? go figure?? I will have to check my speedometer to see if it corrected itself.

 

You can not relearn somethings on the computers. you have to tell the computers what they are going into. I could tell a dakota its a charger and vise versa. most vehicles will need to know things such as gear ratios and tire sizes CEL will go off because you just made the computer stupid for a bit. may work but i would bet it comes back in a little while. and now without the code we dont know where to chase.

 

Thanks to everyone who had suggestions. However, I finally took it to the dealership, who of course was just as puzzled and I have been, after 4 hours the only thing they could come up with is that it needs a whole new computer system. Luckily they got it covered by warranty, however, just took it to them today and another 4 hours later, that was not it! I also took it to autozone to hook up to computer to see why my CEL was on, it said something about catalytic converter or oxygen sensors not putting out sufficiently???? Picked it up from the dealer today and light is off, speedometer is still 10 mph off, slower than it should be. Tire size and inflation are correct. VERY PUZZLING!!! And aggravating. Any help is greatly appreciated.