Long story short, I fixed my scanner today and hooked it up to my 97 C1500 with the 4.3L. The truck keeps firing off a P0420 for inefficient cat. The truck has no misfires, runs great, no exhaust leaks but the post cat O2 is hovering around .0xx-.3xx then upwards of .9xx momentarily but never goes as fast as the other two 02's. That being said, does this sound like a bad sensor or if the converter was bad, would it cause the 02 to be lazy? Just wondering that's all. I don't want to switch 02's for the hell of it unless I know just because they're put near rusted in the pipes.

 

The sign of a good catalytic converter would be to see post cat oxygen sensor readings fluctuate very little. When the post cat readings start to mirror that of the pre cat sensors in terms of voltage and switch transition times the PCM determines that the converter is no longer working efficiently. It is most likely the converter is causing P0420 to set.

 

Oh, see now I would think that it would switch. It's being VERY lazy. It's still moving but mainly never goes above .4xx MV. Hmmm, wish I had a spare sensor to throw in and test it. The truck runs great under WOT. Maybe I should take 2 plug de-foulers and just trick the pCM into thinking the cat is working.......

 

By the way, I should have rephrased my question if a bad cat would cause the 02 sensor to look lazy

 

Had that happen to mine before, I took it off, wiped it off with a damp cloth and put it back in and has worked fine since.

 

Ok, just got back from a test drive. The light is ON AGAIN. At idle it fluctuates between .150-.250MV, while driving it goes no lower than .500-.600mv. If I come to a stop it hangs at .500-.600mv and then as I idle it slowly comes back down to .150mv or thereabouts. Under WOT I saw .902mv. Someone please clarify and explain to me if the post converter 02 is supposed to act like a normal 02. Obviously it plays no part in fuel metering BUT should it be switching like a normal 02? If not, how should it be? If it is, then I have a bad 02. I'm going to try cleaning it in gasoline or some CDC Throttle Body cleaner tomorrow. I've got nothing to lose if the 02 is already bad. If I win, then yay me! This problem only popped up after a misfire developed in my truck (which is now fixed) I drove with the misfire for maybe 120 miles, I can't believe that would be enough to plug the converter (it's brand new magnaflow unit from february). At the same time the misfire occurred, I put 2 bottles of chevron techron synchron in the tank, I wonder if this plugged the 02 up with carbon or something. That's another thing to note anyways. Any info on this guys would be appreciated

 

If it's running good just turn off that sensor and call it a day.

 

HP Tuners doesn't work with '97 Vortec 4.3L PCM's or this would have already been done......

 

No one? This seems to be happening only at highway speeds for an extended amount of time......

 

In my truck, after LT installs, I started throwing those codes. Caused by getting the 02 sensor further back in the exhaust flow causing it to struggle to stay hot. O2's are "Lazy" until they get up to temp. IMO the heater in that O2 has gone bad or is weak. It should switch, or at least they do in my 03. By your description it starts getting lazy at low exhaust flows. A sign its cooling off.