I have a 2002 Lexus ES300 (just like your wife’s) with 96,000 miles on it. 5,000 miles ago it stalled out at a traffic light. I had a P0446 so I bought a new Toyota gas cap. I also noticed one of the small vacuum hoses attached to the T-connection by the battery was loose so I clamped it on. It runs perfectly. The P0446 came on again 2000 miles ago and I just kept clearing it so the check engine light would go off. About 500 miles ago it came back on and I left it alone. Yesterday the check engine light turned off on its own. I love the car. Everything works on it as if it were new. And it’s running as good as ever. Any ideas what is causing this and can it be diagnosed without the check engine light lit?