I own a 1998 f-150 v-8 the check engine light turned on, so Itook it to the mechanic. After the second day he said he found the problem, but he had to drive the truck 100 miles for the computer to reset. Then he would be certain the problem was repaired. My question, is this common? Because it sounds very unusual to me. Am I getting ripped off?
1996 and new vehicles have " monitors" that keep tabs on the emission related components. Somewhat like tests the computer runs on the functionality of the emissions system. Those monitors run at specific times. After a specific temperature is reached. After a certain speed is reached. Distance. Etc. Some won't even run unless other monitors have already run.
If your mechanic disconnected the battery while doing repairs, the computer needs to relearn engine parameters such as fuel trim, and that can only be done by driving the vehicle as you would normally drive it. If he wanted to know whether or not he repaired the problem he was intending to repair, he needed to drive the vehicle, allow the computer to run through it's monitors and see if the problem would resurface since he reset the computer and it had no memory of anything being wrong.
On a lot of vehicles, the check enigne light won't even come on unless the problem occurs two times in a row.
A hundred miles seems like a long way, but he seems like an able mechanic.