P0420 code

Changed both O2 sensors on my 2000 4Runner because I had a CEL code P0171. Cleared the code, got the truck inspected, and thought I was good. That was a Thursday. Monday morning when I started my truck the CEL light was on and reading P0420. The truck seems to be running fine, no sputtering, no rotten smells. If the new O2 sensor was bad, could that throw the code, and shouldn’t have happened quicker? I have a cheap scanner and not one that can monitor O2 levels. Trying to avoid the mechanic. Any thoughts?

 

P0420 code signals a low catalyst system efficiency

Did you buy TOYOTA or DENSO sensors or shitty aftermarket?

Did you test your CAT with an infrared thermometer to see if it is working?

 

I bought DENSO. I haven’t tested the CAT yet. I’ll try that. Thanks.

 

https://www.4runners.com/threads/weird-inconsistant-p0420-situation-fluke-bad-gas-elevation.26169/

The above link has some ideas behind this. Let us know what solution erases your P0420.

 

Cool. In that case, I would check that your CAT is working and if so, just reset it a few times.

You may have another issue that caused the original code. O2 sensors are far down the list for causes of a P0171...but are on the list.

 

Forgot to mention - I changed the O2 sensors first and that didn’t initially clear the code. I pulled out the MAFS and gave it a good cleaning. Then the code was cleared. The old O2 sensors that I pulled out were pretty ashy looking. I just bought the truck a few weeks ago so I figured replacing them wouldn’t hurt.

 

MAF was probably the original issue. When dirty it will produce a lean condition.

My O2 sensor trips that code every year on long trips. I reset it a few times and it stays off for quite a while. I would try that. The only bad thing is the code will just come back.

Did you keep your old sensors? Were the connectors the same as the ones you put in?

 

I have tossed them now, but the connectors were identical.

 

OK, then the sensors should be correct.

When you check your CAT, I would also double check the O2 sensor wires and make sure you didn't leave one touching the exhaust. Since you made this change just recently, it's very likely related to what you've done. Either a faulty wire, exhaust leak, bad ground, or bad sensor.

If you find nothing physically wrong...like I said, just clear the code a few times. I think I finally replaced my O2 sensor when I cleared the code and it just came back almost immediately. Otherwise, resetting seems to work for me.

 

Usually a P0420/P0430 is a bad cat.

Grab a scan tool that reads live data and report the oxygen sensor readings.