Well I knew the 4runner was due for a problem or two since it had been running so flawlessly for so long. I drove home from my inlaws last night and wouldn't you know it, the CEL goes on. I looked at the engine temp immediately and shut off the radio just to be sure I wasn't missing any audible clues. Nope, drove ok, no studdering so I limped the short distance home. Checked the oil and coolant and both were fine so I went in and got my Auterra OBD code reader (that thing is a godsend!!!) to see what the deal was. Plugged it in and right away, the code popped up.
P0141 O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 2)
So since the truck was already warm I used the graphing function to just take a look and see what the front/rear O2 sensor outputs looked like back to back (the front sensor should be a nice sine wave and the rear should be fairly flat at idle near the average voltage for the first.....ie halfway between the high and lows on the sine wave). Well, the front one looked fine, good sine wave (looked to be burning just right, not too lean or rich). The rear one's voltage output was through the roof.....I mean flatline at the top of the graph (solidly over 1.25V) which means that yes, the sensor is definately TOAST. So I called up the local dealer to get a new sensor and they wanted $257 CDN for it......I almost spit out my drink......WTF, are you kidding me?! So now I need to get one shipped from the US because there ain't no way I'm dropping cash like that for an O2 sensor (maybe Evan, Phil or URD might be able to help me out on the cross border deal?!). I can't imagine how much they'd want for an A/F sensor up here, dirty buggers!
Will report once I replace and the code is gone, but I think it's gonna be pretty straight forward. The big deal is going to be getting the nuts off since I am sure they're pretty bad after a few winters up here. I'm gonna try some of the suggestions here and I'll give my verdict on what worked best from what I try.