Dreaded P0420 code on my 2016 Malibu 2.5L

[JTK]

This is an 8th gen 2.5L equipped Malibu. It's got 98K miles on it, runs like a top and has no exhaust leaks that I can see, feel or hear. This code just started about two weeks ago. Of course it's due for it's PR of NY yearly state inspection this month and won't pass with the MIL lit. A CARB compliant replacement CC is in the $1600 range and this is all you can mail order or have installed in NY. She's not worth throwing ~$2K into just this. I don't know if any of the 'cat clean' products are worth a try, or some spacers for the downstream O2 sensor, but I may be trying both. Pretty thrilled about this.

 

[The Critic]

If the code is legitimately intermittent, I would reset the code and drive it just enough to set the monitors...then get it inspected.

In your area I would also make sure that there are no exhaust leaks (from rust) that are causing a false P0420.

 

[Bottom_Feeder]

100k miles is a nice round number to throw O2 sensors at it anyway so that may be worth doing if they aren't a bear to replace.

 

[The Critic]

100k miles is a nice round number to throw O2 sensors at it anyway so that may be worth doing if they aren't a bear to replace.

That’s just a wallet flush. If the o2 sensors are legitimately bad, you will get a fault code.

 

[JTK]

If the code is legitimately intermittent, I would reset the code and drive it just enough to set the monitors...then get it inspected.

In your area I would also make sure that there are no exhaust leaks (from rust) that are causing a false P0420.

This is what I am hoping for.

Next would be a cleaner, then spacers.

I can have out of state family mail order a fed CC and then send it to me for me to install, but I don't care to experiment with $300 and a bunch of driveway knuckle-busting for a temporary fix.

It's a shame as the vehicle runs and drives perfectly and it isn't all rotted out yet. It looks rough due to a deer strike a year or so ago that broke all of the nose plastic and the a/c is barely hanging on due to a bad condenser (it may be flat now).

 

[crashz]

I bought a low mileage truck that had an exhaust leak. The used car dealer did me a "favor" a replaced one of the cats with a new knock-off brand. Fixed the leak. Caused a code. Since they boogered up the O2 sensors anyway, I replaced the two rear sensors (very reasonable price) and added spacers. Viola! Works like a charm and passes inspection.

 

[slacktide_bitog]

Cataclean is $25, which is a lot cheaper than $1600 for a CARB-legal cat

Can you have a cat installed in Canada? I think they go by federal emissions, and I don't think they have any California emissions provinces

If you act quick, Rock Auto has the OE GM cat for only $1200, but there's only one left! Why is there a core charge for a cat?

This is what I am hoping for.

Next would be a cleaner, then spacers.

I can have out of state family mail order a fed CC and then send it to me for me to install, but I don't care to experiment with $300 and a bunch of driveway knuckle-busting for a temporary fix.

It's a shame as the vehicle runs and drives perfectly and it isn't all rotted out yet. It looks rough due to a deer strike a year or so ago that broke all of the nose plastic and the a/c is barely hanging on due to a bad condenser (it may be flat now).

If you have out-of-state family that can get you a federal cat, that works too.

You can get a front cat for your 2016 Malibu Limited 2.5 for $100 on eBay. A lot of those eBay cats are made in Canada. If you don't trust the ebay cat, you can get a better name for under $200 from Rock Auto. They even have one coated black to help slow down the rust!

Though the oxygen sensors throw their own codes when bad, you should still replace them along with the new cat. Rock auto has GM OE sensors at a good price.

 

[The Critic]

If you have out-of-state family that can get you a federal cat, that works too.

That may not work if the technician is required to check for a CARB ID# on the aftermarket cat during inspection.

 

[slacktide_bitog]

That may not work if the technician is required to check for a CARB ID# on the aftermarket cat during inspection.

Correct, but I don't think they do. They most likely just check that the cat is present.

They are probably not as strict as California with having to match the EO stuff

 

[nickaluch]

Check recalls I had one for my 2.4 found the letter from GM in my car file I was just about to drop $1k for new cat.

 

[Rob_Roy]

I think the cleaner and some spirited driving is worth a try, especially if the car has been short tripped. Have the spark plugs ever been replaced? MAF cleaned?

 

[andrew_j]

Reset codes and see if it comes back.

My 07 Acura MDX would show this code every year and I never did a thing about it. It seemed to clear on its own . I owned from 2011-2020.

 

[JTK]

Check recalls I had one for my 2.4 found the letter from GM in my car file I was just about to drop $1k for new cat.

Good point. I bought it as a repaired salvage vehicle two years ago (deer strike front end damage). It could have a 10yr/150K mile CC on it as it is an "Eco" model, but I'm not sure how that would pan out being a salvage vehicle. It could be timed out anyway as I believe it was purchased originally in 2015.

I think the cleaner and some spirited driving is worth a try, especially if the car has been short tripped. Have the spark plugs ever been replaced? MAF cleaned?

They are likely the factory plugs and MAF.

Reset codes and see if it comes back.

My 07 Acura MDX would show this code every year and I never did a thing about it. It seemed to clear on its own . I owned from 2011-2020.

Fingers crossed on that!

 

[2010Civic]

In my experience the P0420 code is more likely to trip when it's cold outside. Maybe in a couple months the code will go away long enough to get it inspected.

 

[RocketRod69]

I have personally done this on 8 or 10 Euro vehicles with the cat code. Pull a spark plug wire, run the engine at 2000 RPM's for a few minutes. This loads the cat with unburned fuel. Hook plug wire back up and pull the air intake hose right at the throttle body. Have a cheap spray bottle handy with water in it. Start engine and run at 2000 RPM while misting water from the spray bottle right into the throttle body. The reason this works: the unburned fuel will cause the cat material to get really hot..and the steam produced from the water will "steam clean" and deposits off the material inside the cat and leave the honeycomb clean and able to do it's job again.

 

[SC Maintenance]

My fronty does that once in a while.

Replace the rear sensor. They can get “lazy” but not throw a code. Not likely it but it’s a cheap try.

Then run cataclean once

Then throw premium gas in it. The premium will let the ECU push the timing ahead a little further - more complete burn. Do a highway run and get the cc nice and hot. If you’re lucky it will set all the monitors before it throws a code. If it does take it immediately for inspection.

Good luck!

 

[ls1mike]

That’s just a wallet flush. If the o2 sensors are legitimately bad, you will get a fault code.

I agree but and you know I am a GM guy, but GM stuff sometimes doing GM stuff. Just chased the same code in my Buick 3800. Plugs, wires and new 02 cleared it. Of course, all those items, as far as I could, tell have been in there for 160,000 miles.

 

[andrew_j]

Don’t dread that code, just bad diagnosis and throwing parts at it.

 

[Nukeman7]

If you act quick, Rock Auto has the OE GM cat for only $1200, but there's only one left! Why is there a core charge for a cat?

There is a core charge for the catalytic converter because the core (if OE) is worth up to several hundred dollars at a recycling yard for the rare earth metals (e.g., platinum, palladium, rhodium). Hence, the proliferation of cat. thefts in the U.S.

 

[Bottom_Feeder]

That’s just a wallet flush. If the o2 sensors are legitimately bad, you will get a fault code.

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