2002 Toyota Avalon

The transmission makes a “clunking” noise when it downshifts into low gear while slowing to a stop. The dealer did a series of diagnostic tests and pulled the pan to check for metal particles. Nothing was conclusive. Translation: The dealer could not get permission to explore the problem further under the terms of the extended warranty. Does anyone have any experience with this problem?

I have had experience with Toyota service being below par if it is something under a warranty. Good merchandise, bad service. I would sure do a transmission service (fluid and filter) on it, if it has not been done recently.