Dreaded P0420 code

Driving home from work and noticed my CEL came on. Pulled over and got my scanner out to see what it was. And it was the code I would always hate to have, P0420. Now they don't check emissions here so I'm not too worried about it. However, seeing the CEL bugs me. I heard using pure lacquer thinner through the gas tank can clean it. Is this true?

 

P0420 is a cat reading is bad I believe so first just get under there and check to make sure you don't have loose or missing bolts on your o2 sensors, it might just be that simple

 

Now that you mention it, i did go over some rough terrain. I'll give that a check tomorrow after work.

 

yep you might have snagged and pulled loose a wire on the o2 sensor even

 

I'll do some examination tomorrow. Thanks!

 

The P0420 code gets thrown whenever there is any emissions issue, from melted o2 sensors to a loose gas cap. Mine came on when a buddy of mine fueled up with 89 (instead of my usual 91) and the code came up.


My advice is to clear it and see how quickly it comes back, if at all. If it stays gone, it was a fluke. If it comes back I'd check the O2 sensor

 

Could it be because of a leaky gas cap? Cause I believe it's original and the seal could be messed up

 

Misfire code?

 

No misfire codes

 

Mine was a rusty gas tank, a hole on top that didn't leak gas.

Don

 

Subscribing to this thread. I had the same code come up as I drove away from the guy I bought my truck from 2 weeks ago (who acted oh-so surprised when I called him about it). Here is the log of my code
2/10 - disconnected battery to clear it. 40 miles later it was back.
2/12 - used scan tool to CLEAR code. 50 miles it was back.
2/18 - replaced CAT (with Walker brand) and downstream O2 sensor (Denso). 40 miles later CEL.
2/20 - started up truck and CEL was gone. Figured the ECU had to learn the new O2/CAT. 30 min. later, CEL was back.

Shop tells me we should try replacing the other sensor and if that doesn't work, change the plugs. Seems so hit and miss.

I don't mean to hijack this thread but maybe there should be a sticky about this P0420 code. This is so frustrating.

BTW - my truck (V6, auto) only has 49000 miles on it.

 

Just cleared it yesterday and drove it a little while. No cel. Hopefully it stays like that

 

To me, this points to a catalytic converter issue. The O2 sensors are reading that the exhaust isn't reacting with the converter as it should. If you've done everything else, I wouldn't be surprised you'll need a new one.

 

I changed the upstream air/fuel sensor last weekend. 400 miles and no CEL.

 

I have same code, it says bank 1. would that be the upstream O2 sensor? I plan on doing a tune up also.

 

Mine was a cracked Rollover valve - don't know how that happened, but the guy who located it for me said it wasn't that common

 

Mine CEL just came on too after replacing the vacuum hose and the gas cap a couple months ago. I can smell a gas odor when I go to the rear of the truck. I'm worried it will be an expensive fix...

 

What kind of cap is it? If it was a cheap one there's a possibility the seal on it is garbage

 

Have you filled it to the top and looked for a wet spot?

My gas tank had a hole up on top, under that rubber pad at the back. It never leaked liquid there, but it was leaking vapors.

Don

 

I threw that code last month. Noticed it after my gas cap FELL OUT

The code went away after putting in a new gas cap...

Got a new gas cap at the dealership for $15!!!