Speedometer Question

Hello Everyone,

I have a problem. My speedometer reads a higher speed than I am actually going. At least 10 miles higher. I recently replaced the differential on my 2000 astro and my mechanic says that it is just a coinsidence. He says that the speed sensor is probably bad. I know it goes on the trans. Can any one tell me how hard it is to replace the sensor. Thanks.

It's probably not a coincidence or a faulty speed sensor. If the gear ratio is different from the original differential, the speedometer/odometer will not register correctly. Take a ride on the freeway and watch the odometer when you pass a mile marker. Travel for 10 miles without changing lanes and check the odometer again. Calculate what percentage the odometer is off. 5% high or low is considered normal. There are two ways to correct it: 1) put the correct gear ratio back in the differential. or 2) reprogram the PCM with a bidirectional scan tool.

A higher ratio will probably also cost you some fuel mileage.