Cat efficiency-P0420-stock

[sw2low]

Try to make this brief, ive read nearly all the articles ive seen in reference to this. Unfortunately most are people who installed catless downpipes.

Stock car. Got the p0420 code, so i bought a rear o2. When i went to install it i noticed the flex had disconnected itself from the downpipe. Returned rear o2 and had a new flex section welded in.

Day +1 after new flex, p0420 comes back.

My question is this, to try an target where to start, i have a slight idle irregularity. Any recommendation which o2 i should try first? I was thinking front cause of the idle.

Thanks guys.

 

[Gimpster]

Do you have any way to scan the vehicle? Looking at the voltage curves of the front/rear o2's is about the only way to do this without just guessing/swapping parts.

If the primary cat has failed, depending on your mileage, you still have emissions warranty left on that.

The primary cat failed on my '13l, they they just replaced it under warranty. They tried to blame the o2's first ($$$ for dealer to do.. not covered by emissions warranty) but I was able to disprove that with scan log data. As an aside, I find it annoying o2's are excluded from emissions warranty. How can you prove/disprove the catalyists are doing their job without a functioning o2? Chicken & egg...

 

[sw2low]

At 80k miles right now.
No way to scan O2 voltages.
Did the front O2. Light stayed off for 200 miles. Back on.
Picked up the rear O2 sensor and installed tonight. Fingers crossed.

So if the light turns back on, that would mean a clogged cat then i assume?
That would mean i would need an O2 extender to keep the light off?

I hate the dealership....but it’s gonna be hard to sell/trade in with a clogged cat and extender.

Yuck.
-RuD

 

[sw2low]

Borrowed a friends scanner.
Are these the two O2 voltages to look at??
At idle 1 would be typically 0.7 v and 2 would be 0.125v or so. But then 2 would increase to 0.7v then back down. I think i have a video too. What am i looking for voltage wise?

Replaced both 02 sensors prior and the same ‘cat efficiency’ code came back...

Thanks guys.
-RuD

 

[PocketRocket]

So I'm having this same P0420 CEL. My sonic just hit 140k miles. I have replaced the cat and both o2 sensors and the CEL keeps coming back on. Since my car is totally stock, would it be worth trying an o2 extender? The voltage on my upstream o2 bounces around like crazy from 0.1 to 0.9. While my downstream o2 hangs out at 0.6-0.8 while on throttle. Any help is appreciated.

 

[Jlsat3]

I have the same problem. Replaced plugs, coil, both O2 sensors, even a new cheap CAT from ebay.

 

[disheveledhair]

No updates? This code is so annoying!