O2 sensor

Purchase an O2 sensor socket ($4) harbor freight. Spray threads with penetrating oil. start engine for about two minutes. slide socket over sensor and turn. I used an iron pipe to slide over the handle of the ratchet.

I see you live in New York, the exhaust hardware may be rusted and tight. Avoid getting burned but I would try to change it when the exhaust is hot because hings will expand.You must use a special socket (any parts store will have it KD tools make the socket about $18). If it doesn't come out try a good penetrating oil like Kroil (WD40 doesn't penetrate well).

There are three 02 sensors on the Sienna van I have.You could not change any with the engine hot. I have a scar where the car underbody sliced me like butter on the middle sensor. All three sensors died within a year (80,000 miles). Went first with aftermarket replacements from Autozone. These replacements didn't make the check engine light go off, which meant I couldn't get a state inspection in Texas. When I bought the parts from a Toyota dealer ($260 vs. @$80 at Autozone), check engine light went off. Replaced all the sensors myself: the front is easiest, the one back on the exhaust is second easiest, the one in the middle is hard to get to and is the tight spot where I got sliced. Autozone shouldn't sell a replacement that won't pass inspection and Toyota shouldn't sell "stealth" parts that you must buy in able to get the cars computer read properly for inspection, and the state of Texas inspection computers should be enabled and programmed to know thte difference.