Test Speedometer/Odometer Accuracy (ASN 0295-01)

TEST SPEEDOMETER/ODOMETER ACCURACY

TECHNICAL SERVICE BULLETIN

TEST SPEEDOMETER/ODOMETER ACCURACY

Model(s): 1986-95 Acura Legend

Group: Electrical

Bulletin No.: ASN 0295-01

Date: February, 1995

SERVICE INFORMATION

A complaint of "speedometer reads fast" can rarely be resolved by replacing the speedometer itself. In most cases, the customer is just keeping up with the flow of traffic, and traffic often flows faster than the posted speed limit. The next most common cause is tires. Underinflated, worn, or undersize tires will make the speedometer read fast, but that's not the speedometer's fault.

If you need to prove the point to someone, find a stretch of highway, with mile markers, where you can safely (and legally) maintain a speed of 60 mph. (*)  Using a stop watch, measure the time it takes to travel one mile at an indicated 60 mph. (If so equipped, use the cruise control to help maintain a steady speed). At 60 mph, it should take 60 seconds to travel one mile. If your time is between 60 and 66 seconds, the speedometer is within our 10 percent tolerance. Customers who suspect that the speedometer reads fast may also be concerned that the odometer is logging more miles than the car actually travels. Actually, there's no correlation between speedometer and odometer error, and odometer error is usually less than speedometer error.

You can measure odometer error at the same time you're checking the speedometer, but it's more practical to have the customer do it because the car should be driven for 10 miles (speed doesn't matter). Reset the trip odometer at the first mile marker, then measure for 10 actual miles. If the odometer reads 10.3 after 10 miles, for example, the odometer error is 3 percent.