Hi, fellas, this is my first post here.
The CEL came on and a dealer wanted $120 to check it. Seems it should be free. This is hard on Social Security. I took it to Auto Zone and the reading came up catalyst system efficiency below threshold, oxygen sensor.
I checked the wiring at the sensors and the colors are not the same as my book. The front one has wh/blue, blue, blk and a wh wire. I get no ground with an ohm meter.
With the key on I get 12.2v at the wh/blue, 2.5v at the blue, 3.02v at the blk and 3.32v at the white. It seems the blk should be ground but I have no idea where a ground point would be.
The front heater shows 1.5 ohms and it is fairly new. It must have been replaced just before I bought the truck, it is a Denso.
I removed both and they were very clean, just needed wiped. The front nuts were not very tight so I suspect a little leakage there.
I put them in tight and cleared the computer.

The rear sensor has wh, red/wh, red and brown wires. The br shows .4 ohms to ground. With the key on I get 12.2v at the wh, 2.5v at the red/wh, .02v at the red and .01v at the brown. The heater shows 13.8 ohms.
Does anyone know what I should do? The truck runs great.

In Google type in - Toyota 5VZFE P0420 - and start reading there are a few things to check. Buckle up for some reading. :bouncy:

http://www.ncttora.com/fsm/2003/index.html That may give you a bit more detailed info than your book that you have now. Basically the sensor is probably bad, however i understand wanting to check things out before throwing parts at it.

They have a new listing for a 96-02 runners (it's for an 02' technically)
http://www.ncttora.com/fsm/1996/SIL/index.html

Thanks guys. From what I see the bank 1 sensor 1 is not an oxygen sensor but an A/F sensor and the heater falls in limits. There is also no ground at the plug.
The light has not come back on so I hope it was the loose nuts on the A/F sensor.
I have to remove each nut and get some anti seize on the threads yet.
I might have to invest in a good scanner.
Can anyone suggest one that won't break the bank?

My 4runner throws the p0420 code on ocasion as well, but only under certain conditions. The first time it happened was on a trail after going through a bit of water, and since its kicked on after a few hours on the trail at slower speeds, but in normal day to day driving its fine.

as far as a scan tool, you can get a cheap code reader from a lot of places, but if you want an actual scan tool that will give you real time data, then i would look into the auto enginuity products, assuming you have a laptop or PDA. There are some other PC based scan tools as well, but i don't have any experience w/ those.

This is one of the differences between California emissions and Non-California emissions spec'd vehicles . If you were not aware that there are two types of exhaust systems out there it might explain why you were seeing wiring color discrepancies.