My wife's second-hand Camry w/ 40,000 mi. has had a constant string of check engine warnings since purchase at 30k. The dealer replaced a cat converter and the light stayed out for a month and then returned. Took it in, they said they pulled three codes and (this is sweet) had to replace the charcoal cannister for the evap system--it could be cracked. Said it would run $650 because an "induction purge" was also needed ($250 for cannister, and $400 for labor and a can of juice in the gas tank). I laughed and told them I'd be up to get the car. Bought a code scanner and pulled 3 codes: 440, 441, and 446. Reset, and the light has not been back on yet. Maybe it was just a hiccup with a vacuum switch. I've got the Haynes w/diagnostic tests for components.
I think the pressure sensor is common to all of the codes, so I'll run a check on that. I thought I'd ask the group if there are any other places where I should concentrate my diagnostic efforts? Thanks much, Mike Davis