96 toyota camry V6LE

My speedometer reads correctly as checked with a GPS. My odometer on a 400 mile trip last week showed the mileage as 639 miles. What is wrong?

There are a lot of reasons such as tire size, but some time ago some car companies were sued for odometers that showed more mileage than the car actually was driven. It was settled without the companies admitting fault. The charge was that they were cheating owners on their warranties and giving false impressions regarding mileage. In the settlement warranties may have been extended, but if so it was a much smaller amount, maybe 5% or so. I suspect your odometer is failing.

That is about a 35% error. It certainly is not normal. Something is wrong. While a GPS can be wrong, it is highly unlikely to be that wrong. Even the conspiracy theories have never suggested them being off that far. It does seen odd to me that the speedometer would be correct and the odometer would be that far off. You may want to do a second check just to be sure, but it sure sounds like a problem.

Sounds bad. Have you checked the mileage chart on a travel guide? I don’t want to suggest that your figures are off but I can’t rule it out when you figure in the nut factor. I’ve heard actual conversations where I wouldn’t believe anything the person said. I have to guess that you have made this trip before without any odd figures. Did you use the right tripodometer? Sometimes there are two of them and one wasn’t reset. If you used the regular odometer, you could have read it wrong when you left. Yes, the doubt factor is huge here.

639 kilometers is almost exactly 400 miles…

In case you were wondering, the odometer mechanism is separate from the speedometer mechanism, at least on cars with mechanical instruments.

So this sort of thing is possible, although I would also suspect measurement error.

An error that large would show up on much shorter trips, so what do you get the rest of the time?

I think you should follow up with what Winarth says. You might have somehow set the odometer to kilometers. Check the owners manual or a dealer.