[sraney]

For those few of you who have been following the "Zen of Oxygen (sensors)" thread, here's the final installment, at least for a while. Led by Zen Master Duffy, I've been exploring what kind of O2 comparator circuitry is built into the ECU, i.e., why does replacement of one sensor seem to almost immediately trigger a code from the other sensor? Does the ECU only compare voltages between the front ones (and maybe between the rear ones), or does it also have some kind of comparison running between front and rear ones as well?

Based upon my empirical research, here are my conclusions (so far). The ECU compares voltage between the right and left front sensors (i.e., between bank 1 sensor 1 and bank 2 sensor 1). This means that if you replace one of the front ones after it's had a few miles (in my case 116,000 miles), you can expect a code to be generated from the remaining "old" sensor within just a few miles simply because of the different response time/voltage/whatever being generated by the two now disparate sensors. However, after replacing the remaining front sensor, I've now logged approximately 100 miles without seeing any codes from the old rear sensors. (Of course, now that I've posted this, I'll probably see a code tomorrow!) Thus, I tentatively conclude that the ECU doesn't care that the front sensors are new and the rear sensors are old. With a little luck, I'll make a few more miles before the rear sensors hit their limits and start throwing codes.

Here's my second conclusion: Replacing these sensors can be really easy, or it can be really, really hard. After soaking in PB Blaster, the first one popped loose with a six-inch ratchet with no trouble. After soaking in PB Blaster, the second one (bank 1--driver's side) resisting cheaters, torch heat, manifold heat, begging, and cursing. It finally took an impact wrench, which, of course, caused minor damage to the threads in the header. However, running a chaser through cleaned it up satisfactorily.

Thanks again to Z.M. Duffy for his previous comments regarding the zen of O2.

Grasshopper