P0420 code - followup:

 

Well, I just wanted to finish up this thread for everyone who will stumble across it using the search function. I had suffered along for more than a year with the P0420 code on for months at a time but every once in a while it would go out on its own only to return in short order. I live in a state where an active code will cause your car to fail it's annual required inspection. So, last year at inspection time I killed the code one week before I had the car inspected. Made it through inspection. With another annual inspection coming up, I had the car on a lift checking everything. I discovered that the right inner CV boot had failed - again. It's the one closest to the cat and gets exposed to a lot of heat. It was at that moment that I thought about replacing the oxygen sensors. On closer inspection it was apparent that there was going to be a lot more room around the front oxygen sensor when the axle was out of the car. So I ordered both the front and rear oxygen sensor after ordering the axle. Getting to the front sensor was easier with the axle out of the way but the grease from the CV joint made the job a real mess.

 

But, I am happy to report that with both oxygen sensors replaced I have not seen the service engine light in over 2,000 miles of driving. I went with Bosch units ordered from Amazon. Their price was lower than most others - around $120 for both.

 

Steve

That's great news Steve.

Please update should the code recur.

I will follow your lead and see if that fixes my intermittent 0420 as well.

Drats!

Recurring 0420 on 05 OB. MY 05 has 5 sensors and three cats. Sensors are located: 2 pre cat, 2 post cat and one atop the rear secondary cat. Under the hood it says Calif. emissions.

I had the 0420 (bank 1 below threshold) so I had already experimented with the cheater on the passenger post cat sensor without success.

Yesterday I installed a new oem pre cat sensor on passenger side (bank 1) hoping that it was getting lazy at 130,000 miles and if so prevent it from damaging the cat if this was the case but the code recurred.

While trying to correctly identify the aftermarket sensors, I spoke with tech support at Bosch who was dubious that replacing the post cat sensor would help in my situation. (Remember it is in his interest to sell more sensors).

He said that this sensor would become slower in response if failing and not more active so less likely to throw code.

I reinstalled the cheater on the post cat sensor in one last ditch effort but it looks like a new cat may be coming in the future to eat out of my wallet!

Edited November 30, 201114 yr by brus brother