P420

[01thunder]

Code popped yesterday. Sensor 1 I replaced 3 years ago. Cats are good. Could it be sensor 2 being 15 years old? Other than this, no issues.

 

[sawguy]

The last time I got that code I replaced upstream and downstream.Problem solved.

 

[highcj5]

with that code, I do believe it is your downstream sensor, since you said your cat was good. I have the same code and need to replace mine as well.

 

[Rock_Rat]

Code popped yesterday. Sensor 1 I replaced 3 years ago. Cats are good. Could it be sensor 2 being 15 years old? Other than this, no issues.

I was getting an intermittent P0420 code for a while. I changed the A/F (upstream sensor) and it slowed down but still came on about every 3-400 miles. Changed the downstream sensor and it would still come on. Normally, the cats are the last things you want to replace just because of the cost and the reliability. However, I just did a complete exhaust upgrade and the code hasn't come back on.

I would definitely change the downstream sensor because of how old it is, (could be faulty) but unless you have new cats installed, it probably won't fix it. The downstream sensor is monitoring the efficiency of the cats. Let's just hope it's faulty.

 

[AZBub]

don't buy crap O2 sensors , stick with Denso. This is a very common thread, with a search you would find its been discussed over and over and over again. the downstream ones can become lazy. replace and go from there.


Sent from my iPhone using Tapatalk

 

[TheDurk]

While a downstream sensor is a likely fix in your case, don't neglect to check for any exhaust leaks between the manifold and the downstream sensor. It can be a really cheap fix. The original gaskets and bolts on these exhaust systems are turning to dust.

I fixed a P0420 by replacing the gasket between the first and second cats on my '99 Cali-spec. One bolt was gone and the gasket was in pieces.