Check Engine light came on in the Tundra. Got the codes run, crossing fingers for loose gas cap, but it came up as a bad oxygen sensor; not the cheaper one behind the cat converter but the more expensive ($140 with 30% discount) upstream one. First thing I did after locating the sensor was to spray where it screwed in to the exhaust manifold with PB Blaster (way better than WD40) and let it sit overnight - oxy sensors are notorious for "freezing" in place, requiring a mechanic to get them off. Easiest way to access was from the underside; after a few minutes of contorting my body to get my hands in a good position, slid the socket on the sensor and darned if it didn't come right off; unplugged it and that was that. Put some anti-seize on the threads of the new one, screwed it in, inserted the plug end into it's receptacle, disconnected the negative terminal to the battery for 30 minutes, re-attached, put the key in the ignition and no more Check Engine light (for now).
It would have been easier with baby-sized hands but really not very difficult a repair and I saved myself about $300-350.

Regards,
Scott