The clinker here is this can be caused by either switch, not necessarily the one that doesn't work one way. That's because there are actually four switches in each switch. When you press the driver's switch, current flows through two sets of released contacts inside the passenger's switch assembly. One of those likely has an arced or pitted contact. The other half of each part of the passenger's switch has one that moves to run it up, or the other moves to run it down. Those two parts are working, as you observed.
The bottom line is the switch that does both functions properly is just as likely to cause this problem as the one that only works one way. Try a different passenger's switch. There's a good chance you can remove one of the rear switches and plug it into the front as a test. On most cars, all the passenger switches use the same shape of plug.
Wednesday, June 5th, 2019 AT 3:49 PM