DTC P0420 - Check Engine Light for Catalytic Converter

[redone17]

I’ll post more details when I can scan for codes tomorrow. But, haven’t heard anyone having the issue yet.

Well, I hit 30,000 miles and got home late last night and had to head out of town all day. I will report back tomorrow once I can scan DTCs. I was parked in NYC and thought perhaps it got tampered with - but I didn’t see any signs upon quick inspection. No noises/sounds, power issues, etc and running fine otherwise.

Any input on what to look for/check is appreciated. Any chance this has something to do with running NGK step colder plugs with the FP Tune?

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[Bronc-Itus]

Just hit 28k. Following

 

[Ducati1098]

Any input on what to look for/check is appreciated. Any chance this has something to do with running NGK step colder plugs with the FP Tune?

Depends on the code, but probably just a faulty converter if it’s P0420.
Very unlikely it has anything to do with the plugs or tune.

 

[Ogre]

Depends on the code, but probably just a faulty converter if it’s P0420.
Very unlikely it has anything to do with the plugs or tune.

Question for a pro, how do you get a faulty catylitic converter? And how do the sensors detect this? It's such a simple part, i don't get it.

As a diesel tech I have to deal with the Regen system and understand the exhaust filter systems, they can go bad. But those are much higher temperature commercial applications. I didn't think they would have much in common. Would a fuel system cleaner like CRC handle this? I did it at 20k and plan on keeping up that pattern with a fuel cleaner every 5k miles.

 

[Ducati1098]

Question for a pro, how do you get a faulty catylitic converter? And how do the sensors detect this? It's such a simple part, i don't get it.

As a diesel tech I have to deal with the Regen system and understand the exhaust filter systems, they can go bad. But those are much higher temperature commercial applications. I didn't think they would have much in common. Would a fuel system cleaner like CRC handle this? I did it at 20k and plan on keeping up that pattern with a fuel cleaner every 5k miles.

Converter efficiency is just based off O2 readings. The less efficient a converter becomes, the less oxygen storage capacity it has. The downstream O2 can detect this in conjunction with the upstream to determine overall converter efficiency. The downstream O2 signal will start to switch more frequently with a less efficient converter compared to a new one.

The main things that destroy a converter are chemical and thermal. So obviously if for some reason the exhaust gasses are abnormally high, the converter will degrade faster. Same with chemical. Oil/coolant in the exhaust, or an engine misfiring frequently dumping unburnt fuel in the converter will also damage it quickly. But at the same time like other parts, sometimes things just wear out quicker than normal even when the engine is running good with no issues.

A fuel system cleaner won’t typically affect the converter. But I suppose the better an engine runs, the longer the converter should realistically last, so it certainly wouldn’t hurt.

 

[redone17]

Thanks for sharing that information @Ducati1098. I would certainly like to learn what caused it if it’s an actual user caused problem.

A few more tidbits of information:

I’ve recently been trying out other gas stations. I was religiously filling up at our local BP with 93 for the past 2.5 years. Reading that they’re no longer part of the Top Tier program I have been trying Gulf, Valero, Shell, etc to see if there is any difference in performance and MPG.

I also have a Magnaflow Catback Exhaust. On cold starts driving down my road (downhill, minimal skinny pedal input) I get some exhaust puttering/popping. As soon as I give it some fuel, it goes away.

Now I’m anxious to read that code. I’ll be home this evening and will report back. I just want to alleviate the service manager pointing any fingers if I can help it.

 

[redone17]

I religiously used additives on my previous diesel VW - but, never thought I would need them for a brand new gas engine. Especially with all of the detergents in modern fuel. But, I guess preventive is better than repair.

I’ve used Techron on other gasoline vehicles. My local dealer included BG 44K in any of their service intervals for our Ranger (I learned that when I used one of our remaining pre-paid oil changes that’s carried over from the Transit).

I guess I’ll choose one and start a regiment.

Redline, Techron, B-12, 44k, Gumout….lots to choose from.

 

[SpringTXOR]

Most of the time a p0420 or cat code does not mean a bad cat. When you purchase a new cat, there is usually a note in there saying to not replace it based solely on that code. That code only means that the sensor data reported back to the ECM is out of range. If the cat is not clogged and you have a tune with different plugs, then I would suspect the tune or non stock plugs are throwing off the exhaust gas mixture that is going through the cat and sensor. Bad gas can also cause it as that does affect engine performance. One thing that is certain though, if your cat has gone bad already the cause of it needs to be fixed before a new one is installed. A converter rarely just goes out, unburned gasoline from inefficient combustion is the main cause aside from just physical damage.

 

[Ogre]

Thanks for sharing that information @Ducati1098. I would certainly like to learn what caused it if it’s an actual user caused problem.

A few more tidbits of information:

I’ve recently been trying out other gas stations. I was religiously filling up at our local BP with 93 for the past 2.5 years. Reading that they’re no longer part of the Top Tier program I have been trying Gulf, Valero, Shell, etc to see if there is any difference in performance and MPG.

I also have a Magnaflow Catback Exhaust. On cold starts driving down my road (downhill, minimal skinny pedal input) I get some exhaust puttering/popping. As soon as I give it some fuel, it goes away.

Now I’m anxious to read that code. I’ll be home this evening and will report back. I just want to alleviate the service manager pointing any fingers if I can help it.

Decel popping is excess fuel. I put Rhinehart headers on my Indian a few weeks ago and it sounded like a babbling brook on decel. Reducing back pressure seems to have a big impact on this part of the tune. Your results make me wary of installing a cat back exhaust like I planned. That 100% more flow MBRP claims may not be a good thing for mostly stock applications....

 

[redone17]

Decel popping is excess fuel. I put Rhinehart headers on my Indian a few weeks ago and it sounded like a babbling brook on decel. Reducing back pressure seems to have a big impact on this part of the tune. Your results make me wary of installing a cat back exhaust like I planned. That 100% more flow MBRP claims may not be a good thing for mostly stock applications....

I wrote Magnaflow to get some feedback from them. They’re always SUPER responsive and helpful in diagnosing issues.

 

[Willub]

Any time I’ve had a cat efficiency code, it’s caused by an o2 sensor failing.

 

[OscarHTX]

Any time I’ve had a cat efficiency code, it’s caused by an o2 sensor failing.

I had this recently in my daily driver. It was the 02 sensors. The catalytic converter had two 02 sensors, one taking readings before the cat and one reading after the cat.

I replaced both as it was easy and cheap and it was fine.

I've also read that taking a lot of short drives over time will cause cats to go out early because they dont get hot enough to do their job. Not sure how accurate that is though as I'm not an expert.

 

[redone17]

Welp, you nailed it @Ducati1098

P0420

I’m trying to attach some sound clips - but, I can’t seem to figure that out. It’s definitely gurgly coming out of the exhaust. I didn’t notice it from inside the cabin that night.

I have half a tank and dropped in half of large bottle of Techron. I’m gonna fill up and dump the rest in tomorrow.

But, this definitely doesn’t sound good.

 

[Bmadda]

Welp, you nailed it @Ducati1098

P0420

I’m trying to attach some sound clips - but, I can’t seem to figure that out. It’s definitely gurgly coming out of the exhaust. I didn’t notice it from inside the cabin that night.

I have half a tank and dropped in half of large bottle of Techron. I’m gonna fill up and dump the rest in tomorrow.

But, this definitely doesn’t sound good.

Cats are 8/80 federal. Leave the code in memory and go get a free one from the dealership! P0420 can't be fixed any other way (that i will discuss publicly)

 

[redone17]

Cats are 8/80 federal. Leave the code in memory and go get a free one from the dealership! P0420 can't be fixed any other way (that i will discuss publicly)

Yeah, I’m calling them in the morning. My coolant was very low the last time I had it in for service. They couldn’t pinpoint why…I sure hope these aren’t related.

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