P0420 - Bank 1

So I’ve noticed there has been many posts about this and I’ll definitely read through them, but I’m quite new to cars and the CEL keeps coming up in our 2009 4-Cyl Tacoma.

Got my hands on a scan tool and I got the infamous P0420 error code. Will try some high octane gas and catalytic converter cleaner this weekend, but in case it’s the O2 sensor, how do I know if it’s Upsteam or Downstream?

Also why is the Upstream one so much more expensive LOL?

Forgot to mention the truck has approx. 160,000 kms on it.

Thank you in advance!

 

You more than likely have a leak in your exhaust manifold. Upping your octane wont fix it. Since your truck is getting up there in age, things are starting to fail. Check for leaks around your headers, then use a borescope and check the condition of your Cat. You could throw another O2 sensor at it but if I were a betting man, id say you have an exhaust leak. With that said, if that's the original 02 sensor, it may have built up enough soot over its life to start showing lean.

-J

 

That code is set by the downstream sensor.
If that is the only code, it likely the converter.
There’s a possibility that an exhaust leak is between the upstream and downstream sensor, so check for leaks there. The sensor itself could be bad, but you need to graph it on a scan tool to know for sure.

My bet is that it’s the converter if that is the only code you have.