On my 2002 Sienna, several years ago, I would get intermittent failures with 0442 and a couple others in the same technical area. 0446 comes to mind. It was extremely intermittent, at times it would go several months without failing. At other times it would fail daily.
A new cap did not help. A new official Toyota cap did not help.
I realized from my own electronics work that it was probably a waste of time to take it to be fixed, since the odds of the mechanic even seeing it were abysmal.
I kept logs. Finally, a man on the Sienna Club said he had two Sienna's and one had the problem. So, he swapped parts from one to the other, and when he swapped the charcoal canister, the problem went with it. He said the assembly seems to have some low pressure, self-actuated valves that may have become sticky.
I took it to the dealer, and requested they replace the canister without diagnosing the problem. They had me sign a waiver that I was taking responsibility for the repair, that if it failed to fix the problem they did not warranty it. I gladly signed, they replaced the canister, and it has been several years now with no more failures.
I worked for some years on military electronics which uses the same sort of "self-test" system that the OBD-II system is, and am quite used to the concept. That does not give me the experience that a good mechanic has, with car electronics, but the shop manual and the Internet are good helps.
by the way, the comments directed to golfnut about changing brands turning on lights, either he is mistaken or lying, OR, his manual does say that. If his manual does say that, I'd sure like to know it.