Scangauge shows different MPH?

[Kurz]

I just got the scangauge yesterday and I installed it today.
So while I was in my Highway cruise I noticed that my Speedometer was showing 55
and the scanguage was showing 51-52.

I was wondering if my Speedometer is off?
Or is the scan gauge more accurate?

I am thinking I should believe what the Computer is telling the Scan Gauge more than my speedometer now.

[fixedintime]

Speedometers can be off. My 95 Honda Civic show 60 mph when my GPS say 55 mph. So yes speedometers can be off. Best bet is to use a GPS, borrow one if needed and do a trip measurement and compare that to the sg trip measurement. The longer the distance the better. Then adjust the sg to match the GPS. If you can't get hold of a GPS you have to either find a very good road measurement (that can be hard as you would like to be within 1% of truth), trust your speedometer, or trust the sg.

[OLD SKOOL]

My speedo is 2 to 3 mph. off too. When it shows 55 I am really doing 52 to 53. On I-5 north of Redding there are speed limit signs that show your actual speed. They all put me 2 to3 under what is indicated. Nice of the state to check my calib.

[HAFNHAF]

just for grins i checked my speedo against my SGII yesterday. within 1 mph. probably within 0.3 mph, but hard to tell. i guess thats because the speedo is electronic, not mechanical, so they are both getting their info from the speed sensor.

[K5ING]

I think that most cars are low by 2 to 3 mph. On my Golf TDI, it reads low by 2.5mph, but the odometer is spot on. It's done for liability issues so you can't blame the car companies for speeding tickets. Calibrate your SG for your odometer, and your speed reading on your SG should be accurate for both.

[fixedintime]

Honda got caught in a class action suit for their speedometer calibration a couple of years back. I think that was part of why my 1995 Civic was off by about 5-7% while the 2005 Accord is within 1%. The case was made that the odometer said 50,000 when you had only gone 47,500 so people were losing out on warranty repairs. They apparently agreed to improve the accuracy without saying they ever did anything wrong.

[PaleMelanesian]

My 04 Odyssey was involved in that lawsuit. The (digidal) odometer reads about 5% high. The analog speedometer is almost exactly right, though. It shows maybe 1% high.

I think, for legal reasons, most carmakers opt to set the speedo high rather than low. If you got a ticket for speeding when your car said you weren't, that would open them up to liability.

[Kinder]

Yes, it is "normal" for speedometers to read higher than actual--my Scion also shows 55 when I am really going 52 or so. The Scangauge is accurate however.

Interestingly the odometer is off the other way! I have to multiply each tank's tripmeter reading by 1.03 to get actual miles. Again, Scangauge is more accurate than the car's digital odometer is. Always nice to get those extra 10 miles added to each tank to boost my mpg.

At least the tachometer on the Scion is correct, though lord knows I wish that read high on the freeway...

[Kurz]

Hmmm... I don't have a GPS so I just adjusted the speed correction a little bit.
Now its within 1-2 mph of the Speedo.

Thanks for everything guys.

I just wish the ECU would send the right value or should I blame the SG2 for not
showing the right value?