P0420 but replaced 02 sens2 40k ago?

[EMBPilot]

About 40K ago i replaced bank 1 #2 oxygen sensor (post cat pax side). All has been well until recently, i reset and got it again; a CEL for P0420 Catalyst System Efficiency Below Threshold (Bank 1)

Since i just replaced that sensor 40k ago im not sure if i should:
- replace it again
- replace both on that side
- or replace front one

I have one 02 sensor handy in the garage not sure which one to take a shot at.

of course i hope its not the cat itself which i guess it could be. Truck is running fine.

thanks again guys
Kevin

 

[2000StreetRod]

Switch Ratio

OBD-II calculates the ratio of the post-cat O2 sensor switching to the pre-cat O2 sensor switching. If the ratio exceeds 0.75 then code P0420 gets set.

Since you have already replaced the post-cat sensor, I would replace the pre-cat sensor.

The chemical deterioration of the cat may not affect performance enough to be noticeable to the driver. How many miles are on the vehicle?

 

[EMBPilot]

just found another o2 sensor. So I'll do both since I have them. I have a hunch it may very well b the cat though since it's the factory one and the truck has 165k

 

[EMBPilot]

update...

changed both bank 1 sensors, 200 miles later, CEL is back on. i guess its the cat after all... grrr

 

[98XplorerSprt]

changed both bank 1 sensors, 200 miles later, CEL is back on. i guess its the cat after all... grrr

How much did it cost you to replace the cat? I've got the same code and I'd like to cover myself on the high side if it isn't the sensors

Actually if I could get 200 miles, all I need to do is pass emissions :hmm:

 

[EMBPilot]

well... the CEL stayed ON for a good few hundred miles... then, all by itself, without me doing anything, it went out, and has been out for at least 6000 miles. no clue what happened. I thought it may have had something to do with ambient temperatures but over the past several months its been anyways from 60 to -15 f and it still hasnt come back.

the cat for that truck is Big bucks, the number i heard from the local muffler place was 4-500. he felt if he had enough room he might be able to put a generic one in but wouldnt be sure till he got under the truck. the generic ones are around $100.

Since its an emissions issue, i really dont plan on addressing it until inspection time (12 months or so) and thats even if the truck makes it that long

Also, when i was trouble shooting it, i was able to reset the CEL, and would be fine for a few hundred miles, maybe just do a reset, take it in for the test. In NJ they cant put AWD vehicles on the dyno so its an easy no sniffer test, they just check the OBD.

 

[98XplorerSprt]

well... the CEL stayed ON for a good few hundred miles... then, all by itself, without me doing anything, it went out, and has been out for at least 6000 miles. no clue what happened. I thought it may have had something to do with ambient temperatures but over the past several months its been anyways from 60 to -15 f and it still hasnt come back.

the cat for that truck is Big bucks, the number i heard from the local muffler place was 4-500. he felt if he had enough room he might be able to put a generic one in but wouldnt be sure till he got under the truck. the generic ones are around $100.

Since its an emissions issue, i really dont plan on addressing it until inspection time (12 months or so) and thats even if the truck makes it that long

Also, when i was trouble shooting it, i was able to reset the CEL, and would be fine for a few hundred miles, maybe just do a reset, take it in for the test. In NJ they cant put AWD vehicles on the dyno so its an easy no sniffer test, they just check the OBD.

My buddy is coming by today with his SnapOn OBDII scanner and we're just going to verify everything. If it is only the P0420 we're going to reset it and see what happens this week. I have to replace the windshield anyway so testing this week will be interesting.

Not sure if you can pass NJ emmisions fresh off a reset, pretty sure there is something that tells the computer the ECM was just reset...but I may try it regardless.