My Mysterious Check Engine Light Caper

[HappyHooligan]

So after 9 months of ownership and daily driving, one 3000 mile cross country trip, when I came home yesterday the mysterious Check Engine light came on!
So being a 3rd gen owner, I immediately ordered a reader off of Amazon. I'd been putting it off and now i need it. So today it's suppose to arrive.
Anyone have any guesses to what it might be before I hook up the reader?

I'll post more as the mystery unfolds.

 

[phattyduck]

P0420

-Charlie

 

[HappyHooligan]

P0420

-Charlie

And I just passed Smog in CT last week...

 

[jgue467]

Oh CEL Bingo/Lottery cool.....Here's to hoping it's Not a P0770.... :cowboy:

 

[HappyHooligan]

P0420

-Charlie

Charlie wins!

Now to figure out what a P0420 code means.

 

[sugjavier]

Charlie wins!

Now to figure out what a P0420 code means.

I solved mine with a new denso Oxygen O2 Sensor. Pretty cheap on Amazon. Like $35 or less. Takes 10 mins to install provided you can get it out without breaking anything due to rust or something

 

[HappyHooligan]

I solved mine with a new denso Oxygen O2 Sensor. Pretty cheap on Amazon. Like $35 or less. Takes 10 mins to install provided you can get it out without breaking anything due to rust or something

was that the rear or front one that fixed it?

 

[sugjavier]

The downstream one which I believe is closer to the rear.
I checked my order history and it seems the price was actually around $50

https://www.amazon.com/gp/aw/d/B0016NBBQW/ref=oh_aui_i_sh_in_o1_img?ie=UTF8&psc=1

 

[TheDurk]

The downstream one which I believe is closer to the rear.
I checked my order history and it seems the price was actually around $50

https://www.amazon.com/gp/aw/d/B0016NBBQW/ref=oh_aui_i_sh_in_o1_img?ie=UTF8&psc=1

That won't fit on his 2000.

 

[kevinRR]

Charlie wins!

Now to figure out what a P0420 code means.

It means your cat is bad or your o2 sensor is bad. If I have to take a guess I go with the cat since the car is almost 20 years old. But there is a way to check if you have a scan tool that can log.

 

[TheDurk]

It means your cat is bad or your o2 sensor is bad. If I have to take a guess I go with the cat since the car is almost 20 years old. But there is a way to check if you have a scan tool that can log.

That said, anyone who puts in a new cat will want to install new sensors, so might as well start with the rear sensor, just in case that is all you need. These cats rarely die on their own, something has to kill them, i.e. physical damage, excess fuel leading to elevated temps, etc.

That said, the FIRST thing to do is check carefully for any leaks between the downstream sensor and the manifold. That is often the cheapest fix. The exhaust gaskets and flange bolts on these rigs, if factory, are turning to rusty dust as we speak, and are a frequent cause of P0420s. I have had two P0420s, one was a gasket and the other was a rear sensor. I'm still on factory cats and no codes.

 

[StreetCreeper]

I know this isn’t helpful...

I like to imagine that the P0420 code is really just your cat gettting stoned

 

[Ed_C]

That's one fat *****...cat