Dreaded P0420 code on my 2016 Malibu 2.5L

[SC Maintenance]

I'm not saying they may have gone 'bad', but they may be lazy, dirty and inaccurate.

Your correct. They get coated and their response time slows - especially if you’re burning any oil. The cat is likely shot , but it’s possible a now sensor will buy you an inspection. The rear sensors seem to take forever to throw their own code , unlike the A/F sensors in front.

 

[The Critic]

I'm not saying they may have gone 'bad', but they may be lazy, dirty and inaccurate.

I disagree. If the deterioration is meaningful, you will set a fault.

Also, if anything, new sensors will perform better and set the P0420 more quickly.

 

[Chris142]

Most of the time a 420 code is a cat that's not working up to snuff. I have seen it caused by another problem where the cat was unable to cope with another problem and threw a 420.

 

[panthermike]

Good luck hopefully easy fix. Ended up putting a spark plug fouler on our Corolla due to a persistent 420 code. 8000 miles later still holding up

 

[Doc8404]

If it runs as well as you say, $1600 might be worth it.

I just sunk $5k into my 2012 Altima I’ve owned since new. 140k miles.

Nothing wrong with her and buying a used car for $5k with unknown issues would be a gamble.

 

[D60]

I'm not saying they may have gone 'bad', but they may be lazy, dirty and inaccurate.

You should at least graph it then. That said, this is more effective for Luddites like me when there's a B2 to compare

 

[mattd]

You need to graph upstream and downstream 02 data. You’ll get your answer pretty quickly that way what the problem is

 

[zzyzzx]

Can you get away with using an O2 spacer in NY? I used one for years here and it worked great.

 

[JTK]

Can you get away with using an O2 spacer in NY? I used one for years here and it worked great.

You can. It might only be an issue if a shop was observant enough to discover emissions equipment had been tampered with.

Turns out I very much lucked out. The P0420 and P305F codes had stayed clear long enough for me to get the vehicle inspected today. I just picked it up. $38.24 total. $21 for the NYS inspection, $13.50 to jamb a plug in the right rear tire due to a nail / slow leak. Everything is A-OK for now and she lives on towards year 3.

That battery correlation code is a real pain with this gen. It pops up very intermittently after an auto stop/start cycle. It's got a new-ish (giant) under hood battery and has a small (motorcycle type) battery in the trunk due to the A/S/S. Problem with my trunk battery is a previous owner hacked the OEM one out and cobbled in small cables and an actual motorcycle battery. There's no way to shut off the A/S/S on this gen other than shift it manually, which is again a pain on this model as you actually have to +/- through the shifts. Those hood switch bypass harnesses set off the MIL on this particular model.

 

[chexxers]

dito on the cold with a 2011 fronty V-6

 

[JTK]

Now almost year later and the Malibu's state inspection due this month, I ordered a set of Doorman 42002 spark plug non-foulers. It's a package of two of them. It was a huge no-go as they are not deep enough to accept the downstream O2 sensor. I returned them and ordered a set of 42109's that are extended length. I'll post back with my results. The 'ol Malibu isn't looking pretty, but has about 107K miles on her currently. It runs and drives excellent..

 

[E150GT]

I have been going through intermittent po421 with my Mazda. I found my fuel trims are out of whack and my mass airflow sensor has been not reading accurately. Replaced maf and I've been watching fuel trims get better and hoping that solves the catalyst code

 

[JTK]

Just an update on my spark plug anti fouler install on my 2016 Malibu. So far so good! All monitors eventually ran and ~6 weeks after install, still no P0420 code. The car passed NYS inspection today. The Dorman 42109's came in a pack of two, so I threaded the 2 of them together, which pushes the downstream O2 sensor about 3-4" out. There was plenty of room to do so on this application as it's angled up into the engine bay, so its not hanging out in harms way. Good for another year. If the CC is truly "bad", it's a shame because this 2.5L doesn't burn any noticeable amount of oil between 5K mile OCIs. It runs like a top. Always has.

I'd be curious to see how live data looks with these spacers in place compared to a known good. As long as the ECM is happy and the MIL isn't lit, I'm happy.

I was able to keep that P305F battery correlation code away by installing a new auto stop/start battery in the truck (it's the size of a motorcycle battery).

 

[D60]

Now almost year later and the Malibu's state inspection due this month, I ordered a set of Doorman 42002 spark plug non-foulers. It's a package of two of them. It was a huge no-go as they are not deep enough to accept the downstream O2 sensor. I returned them and ordered a set of 42109's that are extended length. I'll post back with my results. The 'ol Malibu isn't looking pretty, but has about 107K miles on her currently. It runs and drives excellent..

You can drill 'em out. Put two together for more length as yeah, they're pretty short.

I use a lathe but since you've already got a pilot hole with a nice c-sink, a hand drill will certainly get you there.

 

[panthermike]

Just an update on my spark plug anti fouler install on my 2016 Malibu. So far so good! All monitors eventually ran and ~6 weeks after install, still no P0420 code. The car passed NYS inspection today. The Dorman 42109's came in a pack of two, so I threaded the 2 of them together, which pushes the downstream O2 sensor about 3-4" out. There was plenty of room to do so on this application as it's angled up into the engine bay, so its not hanging out in harms way. Good for another year. If the CC is truly "bad", it's a shame because this 2.5L doesn't burn any noticeable amount of oil between 5K mile OCIs. It runs like a top. Always has.

I'd be curious to see how live data looks with these spacers in place compared to a known good. As long as the ECM is happy and the MIL isn't lit, I'm happy.

I was able to keep that P305F battery correlation code away by installing a new auto stop/start battery in the truck (it's the size of a motorcycle battery).

Good to hear! Been on the Corolla for about 21,000 miles, has not returned!

 

[PandaBear]

I have combated a V6 Camry with a bad CARB cat due to owner abuse (did not fix starter and just keep cranking the engine to start). I have tried and got it to pass smog in California as needed without modification, but unless I put a long spark plug anti-fouler on it they will eventually return.

To get mine to pass without fixing anything I would drive it with a bottle of Techron (or maybe acetone would work too but I don't want to risk dissolving gasket somewhere), drive on highway to trip the drive cycle, new cheap plugs, fresh oil change, Drive it to the CEL goes off then go smog immediately or the next day as soon as the engine warms up enough to test but not enough local driving to trip CEL again. New oil and new spark plugs help, but not enough to make up for a worn cat over long term. Mine was OBD2 but before 2000 so it still need to do tailpipe test. If it is a newer one like 2016 you likely only need to scan it without tailpipe sniffer. As long as the visual pass and no CEL it would pass.

The spark plug non fouler restricted the airflow to the downstream O2 enough that it looks like the profile of a functional cat. The only problem is failing visual. If you are handly you might be able to make a custom shield over the O2 to restrict some if not all the flow to the O2 like a non fouler, but small enough to connect it inside the pipe without showing it to the technician. Or, drive daily with a non fouler till right before smog and take it off just for smog to pass visual. It probably is a lot of work and is not worth all that if you can buy a CARB cat for cheap. I think mine is probably around $500-600 on Rock Auto, it doesn't have to be OEM, a Walker universal CARB cat may work as long as you can find a shop to weld it on.

In the end I sold that V6 Camry right after passing smog and told the new owner about this. I sold it for a cheap enough price that if it fail smog next time, our air quality district will buy it off him for the exact price I sold him. He would not lose any money for it.

 

[JTK]

You can drill 'em out. Put two together for more length as yeah, they're pretty short.

I use a lathe but since you've already got a pilot hole with a nice c-sink, a hand drill will certainly get you there.

The first set of dorman anti-foulers I bought could have been drilled out to accommodate the O2 sensor. It wouldn't fit otherwise. I opted to return them and order the "long barrel" Dormans. With the two of them threaded together, the sensor is way out of the direct exhaust stream.

.... If it is a newer one like 2016 you likely only need to scan it without tailpipe sniffer. As long as the visual pass and no CEL it would pass.

Yes, luckily we've never had exhaust analyzers in the PR of NY. Just the OBDII scan, monitors must be set and no MIL present. The shops I go to would either not notice the spacers or if they did, they'd ignore them.

 

[D60]

The first set of dorman anti-foulers I bought could have been drilled out to accommodate the O2 sensor. It wouldn't fit otherwise. I opted to return them and order the "long barrel" Dormans. With the two of them threaded together, the sensor is way out of the direct exhaust stream.

Yes, luckily we've never had exhaust analyzers in the PR of NY. Just the OBDII scan, monitors must be set and no MIL present. The shops I go to would either not notice the spacers or if they did, they'd ignore them.

I like the mix 'n match aspect....sometimes I'll put long with short, like stacking socket extensions. IOW, good to have both