Originally Posted by n3elz
Welcome! Bob can find anything, lol.
On those older trucks, you're not really resetting a sensor, just a "counter" that automatically triggers at a certain mileage. The reason was because the EGR valves in those days were pretty crappy and had to be serviced or replace periodically. I may be wrong about what it was for, but that's basically the idea even if it wasn't EGR.
I don't know either, John. In the old days, many manufacturers had a service interval on the oxygen sensor(s), too. Often the interval was set at 60K, just outside of the emission component warranty (5/50k), relieving the manufacturer of the responsibility for replacing it ....