incorrect speedometer reading

Is it possible that you pressed the button that switches from mph to km/h?

 

40 kmh is slower than 40 mph, by a factor of roughly 5/8. So if it was inadvertantly switched to kmh, and the speedometer read 40 (kmh), that would be something like 25 mph.

 

Not knowing what kind of difference you're talking about, did you replace tires? That can throw it off a bit. My Pirellis were spot on but when I switched to my current Yokohama tires the speedometer now reads 2 mph high at 70 mph compared to GPS mph.

 

How do you know this? Are you comparing the displayed speed to a known good reference like GPS? If so, how much is the speedometer off at indicated 40 mph on the speedometer?

 

That's sound advice. Still:

If OP's driving around the posted speed limit, and he's going faster than most other cars on the road, that seems VERY weird.

I recall many years back, I'd just got my license and was commuting by car for a while, I seriously wondered if my speedo was off too, except this was because everyone was passing me. Now that's normal, lol.

 

As I brought home the first car purchased with my own money (vs. handed down from parents), I had this experience too. I soon figured out that its speedometer was very significantly over-reading, something like 4 mph off, back during the National 55 MPH speed limit days. Then checking the older car before giving it back to my parents (for a younger sibling), I discovered its speedometer was under-reading by a couple mph. So the difference between those two cars' speedometers was about 6 mph. Fortunately that under-read on the first one had never caused a speeding ticket.

That under-read is unheard of these days, though could have been related to a prior accident repair (before I had it). The over-read on the other one would be abnormally high today, but was probably within the normal range back in the old analog days.

 

How are you verifying this speed difference?

 

OK, I'm reading the "but cars not moving that fast" as "but car's not moving that fast." As in reading 40 mph, but the car is not moving at 40 mph.

I had the same thing happen this morning, I saw I was doing 80! Now, I don't do 80, especially on the road I was driving on, so I checked with Priuschat. I didn't want to revive a 9 year old thread (Speedometer Wildly Exaggerating Speed. | PriusChat), but I just saw this one.

So yes, what had happened is I was going 80 km/h, which works out to 48 mph, exactly what I'm usually driving.

And as has been mentioned, there is the little km/h button under the MFD, at least on my Gen2 Prius.

 

i have a 2019 Prius Prime and the speedo and odo are both incorrect. 115 and 97.78km vs 120 and 100.1km
I have to assume the GPS on the left is accurate since i verified with another GPS.This seems like a fairly major flaw, since many things depend on an accurate odometer reading, warranty for starters, maintenance intervals, fuel economy ratings etc etc. Im going to contact my dealer where i bought the car and insist this be fixed. It does not need to be perfect since the wear on the stock tires may cause some very minor discrepencies over the life of the car but the current amount of error is unacceptable.

 

A small over-read on the speedometer is the industry norm. It is essentially forced by law in much of the world, where some error is a fact of life but many laws or regulations forbid any error on the under-read side. So the car makers bias the reading slightly high.

The speed error you are showing is 4%, not unusual for North America, while European market vehicles often have even greater errors, pushing 10%. The likelihood of getting the dealer to 'fix' the built-in factory offset is essentially nil. If you succeed, many readers here would like to know just how it gets fixed so they can replicate it. A few have 'fixed' it by installing slightly larger tires.

Many of us have found that the car's internal computers know the speed more accurately and don't include the intentional dashboard display bias or offset. This internal measure can be read with an aftermarket OBDII-port monitor. I use a ScanGauge-II, but there are many other similar but newer products, and most folks now use smartphone apps coupled with a Bluetooth-OBDII dongle.

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Odometer error is a whole different matter. In the U.S., odometer accuracy is 'regulated' by class-action lawsuits from the product defect and liability 'industry'. Several car makers with odometers reading too high were hit with warranty fraud claims. Their settlements gave 2% warranty extensions on the mileage portion, something better for the lead plantiffs, and a pile of cash for the lawyers. And to prevent future claims, their later car models have odometers reading slightly lower than actual distance.

I've had two cars the fell under such lawsuits, despite my units not having the alleged defect. One was later replaced by a model of the same brand, and its odometer reads 1.8% low.

I don't know how odometer accuracy is regulated in the rest of the world, beyond the reach of American tort lawyers.

 

Let's start here. What did you replace?

 

This will prove to be extremely frustrating for you. Just accept it as a fact of life and you'll be much happier. Next time you get tires, get one size larger and it will pretty much even out.

 

Your in the Gen 2 area bro. The last gen 2 was built in 2009. That’s 10 years before your car was built. Try asking your question in the correct forum.

 

^ It is looking like a "One and done" poster. Hasn't yet returned to check for any responses.

 

Two in the same thread? Impressive. I see that the OP still only has one post to her or her credit.

 

In hindsight, I mighta got suckered in by the lack of an apostrophe in "cars" (I just added it, in the quote, in red). OP is maybe saying his car is not moving that fast? Then the inadvertant switch to KMH makes sense.

OP gone, no problem.