Honda Repair: 98 Civic EX speedometer inaccuracy readings, legal speed limit, speedometer accuracy

Question
Hello.

I own a 98 Honda Civic EX with almost 100,000 miles. I'm having a problem with my speedometer reading 5 mph faster at higher speeds, than what the car is traveling at. This was confirmed by using a handheld GPS. At slower speeds, the speedo is close to accurate, but as the cars speed increases to around 60 mph, the reading becomes more inaccurate.  I've tested the VSS per a Haynes manual, and it pulses 0 to 5 volts when I rotate the front wheel.  I suspect the VSS is working correctly, but it's hard to test something with just a voltmeter.  There isnt a "check engine" light and the tires and wheels are spec. No other mods have been done.  Is it possible to still have a faulty VSS? If not, can the speedo be calibrated to the sensor?  Also, Ive done some research and found most speedometers read faster and theres a + or - 10% factory spec which allow for this and is acceptable. Your ideas on this are greatly appreciated.

Thanks,

Dale  

Answer
Directly from Honda :)

Test Speedometer/Odometer
Accuracy
If your customer complains that when driving the speed limit according to their speedometer, motorists behind them are trying to pass or are signaling them to move over, the problem may be a speedometer that's reading too fast. But before you go and replace the speedometer, consider this: Traffic these days often flows faster than the posted speed limit. So if you're going the legal speed limit by what your speedometer reads, but you’re not keeping up with the flow of traffic, the speedometer may be working properly �it just
seems you’re going slower because all those other drivers are speeding. And something else to consider: the vehicle’s tires. Tires that are underinflated, worn, or undersized, will make even an accurate speedometer read fast. If you need to check speedometer accuracy, find a stretch of road, with mileage markers, where you can safely (and legally) drive steadily at 60 mph. While driving at a steady 60 mph (set the cruise control if the vehicle has it), use a  stopwatch to measure the time it takes you to travel 1 mile. If the measured time is between 60 and 66 seconds, the speedometer is OK; it’s within Honda’s 10 percent tolerance. If you want to test the speedometer at other speeds, divide 3,600 by the number of seconds it takes to travel 1 mile. The result is the average speed, which you can then compare to whatever the speedometer showed. Customers who suspect their speedometer reads fast are often concerned that the odometer is logging more miles than the vehicle travels.
Assure your customers there’s no connection between speedometer and odometer error, but if you need to check the odometer’s accuracy, here’s a way to do it. Although you can do this check while youÂ’re doing the speedometer check, it’s more practical to have your customer do it, since you need to drive the vehicle for a distance of 10 miles (vehicle speed doesn’t matter here). Reset the trip odometer at the first mileage marker, then drive for a full 10 miles. If the odometer reads 10.3 miles after going 10 miles, the odometer is OK; it has an error of 3 percent, and it’s within Honda’s 3.5 percent tolerance.

Hope that helps.