2002 4x4 3.4l V6 Throwing PO420 CEL Code

So around 3 months ago i first got this code and ended up replacing the upstream o2 sensor. This solved the problem until today when I was just driving down the road and it kicked on. Got it read again and got the same code. While it may be the CATS since my truck has 150k miles on it, i thought to myself that it couldn't be since the frame was replaced in august of 2009 and the exhaust was done at the same time. What else should I look for?

 

What type of sensor did you use? If it was anything other than a Denso oem sensor......that's likely the problem.

 

Shit, I used a Bosch (sp?).

 

yeah man.....our trucks dont like aftermarket sensors or catalytic converters at all.

go to rockauto.com........prices are awesome versus the stealership...and customer service is great as well.

 

Was the cat replaced as part of the system? It may still be original. Have you smelled rotten eggs or something funny as you've been driving recently? If so, the cat has probably failed.

In my experience having the cat replaced by the dealer under warranty (though it was a Miata) the dealer will fight you tooth and nail not to replace the cat, even if the signs are there - smell, barely passing emissions, and the p0420 code which points directly to the cat. The dealer actually refused to replace the cat until I replaced the second O2 sensor (on my dime, of course). However, if the O2 sensor is new, the cat may actually be bad. You may try clearing the code and seeing if it comes back.

 

I cleared the code yesterday but it came back roughly 45 miles later. Might have 2 go with a new OEM o2 and see what happens from there. Thanks for your help.

 

do the downstream 02 sensor too, thats what cleared it for me

 

This may be a hijack but - on my 165K 2001 3.4L dbl cab
I had a p0420 code so I replaced the upstream O2 sensor a month ago, with Denso.
My CEL came back on this week and I am still getting a P0420 code -
I think i should replace the rear O2 like fireturk41 recommends, as it is OEM and maybe just wore out - any opinions?
No rotton egg smell to indicate the Cat is bad...

 

9 out of 10 the down stream o2 sensor is gonna be bad

 

Okay, o2 sensor will be replaced.
Does anyone have the Denso stock # for the down stream sensor?
Thanks!

 

part #2344189 for the denso down stream o2 sensor that can be found on rock auto for the 3.4l

 

Im not getting a rotten egg smell or any other indications of a bad CAT either. Looks like I wasted $180 on that bosch sensor and i'm going to get the OEM one and hope for the best.

 

it actually is a good idea to replace both front and rear sensor at one time.....if you can afford them. i did mine back last year,......no probs since.

best place to get them is rockauto.com. they are vendors here and you may can get a discount.

 

So let me get this straight...

Aside from the smell of rotting eggs coming out of your exhaust, there is no other way to point the finger in a more technical way directly at faulty cats (not to mention which of the two cats) before spending the money on 02 sensors when a P0420 code is triggered?

 

Thanks - ordering immediately!

 

One last quick question: http://www.rockauto.com/catalog/catalog.php?carcode=1388987&parttype=5132 If you go to that site and look at the upstream o2 sensors denso makes 2 of them. They have the same info but the part number differs slightly and so does the price. Which one should i go with?

 

just pulled the receipt out of my records for my truck and the Denso upstream # I used was

$145 234-9001 Upstream Air Fuel Ratio Oxygen Sensor with 10.6” 4-Wire Harness, for Auto Trans Equipped Vehicles

234-9001 from Amazon it was about $100 - the stealership wanted $230!

 

You can do an emissions test on your vehicle with tail pipe sniffer test. It reads the amount HC's and CO's in your exhaust. If your HC's are through the roof then the cat is bad. Usually have to go to a repair shop that is emissions certified, or go to your local department of air quality and get it checked.

I'm emissions certified in AZ and do these test's regularly. It's VERY obvious if the cat is bad.....

 

See if you can return the bosch, tell the parts guys that it's obviously bad because the code went away when cleared, then came back. When I worked auto parts we pretty much had to take the customer's word for it on those kind of parts since there is no way to test them.

If the code specified that it's the upstream sensor, then that's got nothing to do with the Cat.

Edit: nevermind, see my post below.

 

Just googled p0420 code and it says catalytic converter efficiency below threshold. I'm going to retract my opinion now and say you should do what this guy says. The computer is looking at the difference in readings between the two sensors. Either the Cat is weak, or one of the two sensors is bad. Seems like the Cat would be easiest to test with any type of accuracy.