help with recurring P0420 code

so, it all started with a P1155(faulty downstream o2 sensor).
I did replace it, but had to graft the new sensor to the old wiring because the sensor I ordered wasn't exactly the right one (wires were too short) and I didn't bother to return it.
I did replace the upstream o2 sensor as well (because at 184k, why not?).

Then I got a lovely P1130. Turned out the upstream sensor was in fact an air/fuel sensor... I did put back my old sensor that was still good.

and since then I have recurring P0420.....

I do not seem to have exhaust leak before the catalytic and sensors. Only thing I could see is my muffler, which is connected to the exhaust piping with exhaust clamps... but this is way after the catalytic and sensors...

Is my catalytic bad? well, I do not seem to have symptoms of a bad cat either (no smell or sounds)... but anyway, is there a way to test it?

The o2 sensor, it has 4 wires (blue, white and two black), so is it possible I did reverse the black wires when I grafted the sensor to the old wiring? Do they have a specific polarity (+ or -) or it doesn't matter at all?

Then I must add that my truck has always had some kind of rough idle. Could it be the TPS sensor? Sparkplugs can be ruled out because they are brand new. No sputtering, hesitation or misfiring either.

 

Just how did you get the wrong sensor??

You did go with Denso ??

I am guessing you used the EWD to wire this new sensor??

My guess is wired wrong

Non California Spec??

 

yes, I went with denso. Since there is so many sensors, I went to my toyota dealer to check what was the part #, so I could order it online. I guess the dude gave me wrong part number or that it was listed with wrong part # on ebay, or it was labeled correct, but wrong part. I don't know really...

yes, I did, but I am wondering if I still did reverse the two black wires?. The sensor is the same after all, but it's the wires that were too short.

you tell me. I guess I'm both federal and cali ??
Also, I'm in canada, so to hell with california emissions... but will my truck be unhappy about putting non cali parts?

 

update:
Since it was my father who did replace the downstream sensor, I decided to remove it and check it just in case and dun dun dun! it was full of muffler cement compound thing
That wasnt helping at all....The sensor couldn't read the catalytic converter output properly! Cleaned it up and put it back. I'll see what it does...

as for the black wires (heater element), the polarity is unimportant, according to the installation instructions

 

If you're still chasing this code:

Check your MAF sensor. I had that code pop up a few times, turned out to be a ton of build up on the lead filament, sprayed it with MAF cleaner till it was clean, let it dry, and put it back in. no issues since.

 

yeah, that's like the first thing I did. But still, thank you for the suggestion

Code hasn't come back since I cleaned my o2 sensor that was full of mufller cement, so fingers crossed

 

woops, stumbled on my old thread while looking for something here on TW and noticed I didn't follow up with my P0420 issue. It never came back after cleaning the o2 sensor of the muffler cement. Dirty sensor was the culprit. Case closed

 

Glad you got it sorted out!!