P0420 code

[Performance nut]

So it seems I'm getting constant P0420 codes on my Kooks Green Cats :rant:

I called Kooks and got :shrug:

So I'm looking for some education. When I researched the code, it talks about doing a waveform comparison between the front and rear O2 sensors. My mechanic said that sometimes the computer is waiting for a response from the rear sensor (which is now further back) and it times out.

• I would figure headers would cause a constant check engine light if the catalytic converter was not present or not effective since the comparison starts when it goes to closed loop control. Is this correct? The reason I ask is because it is intermittent. I can drive for days and not get it and then bam, check engine light.
• Is there something I can check that may be loose or improperly connected?
• I always get the same code, would it mean that it is just one converter/sensor giving me issues?

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[Terminator2]

Seems like most with smaller than stock cats (high flows and even the green cats) get the cat ineffiency codes P0420 (bank 1) and P0430 (bank 2). There are quite a few who have posted threads on this with the kooks green cats.

 

[Randy954]

You will throw that code if the cats areant efficiently decreasing emissions. Unfortunately most hi flow cats will cause that.

Also the cat monitor doesn't always come on right away and u have to drive certain drive cycles before it will notice the issue of the hi flow cats. If you don't do much highway driving the cat monitor won't kick on very fast so that's why it's taking a few days to throw the p0420 code

 

[Jn2]

Almost all hi-flow cats will throw a P0420/P0430 code for catalyst efficiency. You need a tune to correct this.

 

[WhiteyDog]

So it seems I'm getting constant P0420 codes on my Kooks Green Cats :rant:

I called Kooks and got :shrug:

So I'm looking for some education. When I researched the code, it talks about doing a waveform comparison between the front and rear O2 sensors. My mechanic said that sometimes the computer is waiting for a response from the rear sensor (which is now further back) and it times out.

• I would figure headers would cause a constant check engine light if the catalytic converter was not present or not effective since the comparison starts when it goes to closed loop control. Is this correct? The reason I ask is because it is intermittent. I can drive for days and not get it and then bam, check engine light.
• Is there something I can check that may be loose or improperly connected?
• I always get the same code, would it mean that it is just one converter/sensor giving me issues?

I believe it was you a few weeks back that was having this issue, wasn't it? Man, that's screwed up. I never had a code, ever. Mine are the Kook's 1-7/8" catted, but I don't have the "Green" cats. I have whatever the other ones are.

 

[2015 Silver GT]

I believe it was you a few weeks back that was having this issue, wasn't it? Man, that's screwed up. I never had a code, ever. Mine are the Kook's 1-7/8" catted, but I don't have the "Green" cats. I have whatever the other ones are.

You aren't throwing a code because your tune from Lund has the rear o2's turned off. If you have emission testing you'll never pass.

 

[Performance nut]

You will throw that code if the cats areant efficiently decreasing emissions. Unfortunately most hi flow cats will cause that.

Also the cat monitor doesn't always come on right away and u have to drive certain drive cycles before it will notice the issue of the hi flow cats. If you don't do much highway driving the cat monitor won't kick on very fast so that's why it's taking a few days to throw the p0420 code

This is what I'm looking to get info on. How is the code generated? After reading about it, it should pretty much come on when the system goes to closed loop (which should happen a few minutes after starting the engine). So I would expect to see it every time I drive but it doesn't. I can do highway driving for an hour and nada. City driving (stop and go) for 15 miles and nada. Drive 100 miles in both stop and go traffic and 70 miles per hour highway driving and get no check engine light.

And then at random, do any of the same things and get a check engine light. Seems random more than the system doing its job.

 

[Randy954]

This is what I'm looking to get info on. How is the code generated? After reading about it, it should pretty much come on when the system goes to closed loop (which should happen a few minutes after starting the engine). So I would expect to see it every time I drive but it doesn't. I can do highway driving for an hour and nada. City driving (stop and go) for 15 miles and nada. Drive 100 miles in both stop and go traffic and 70 miles per hour highway driving and get no check engine light.

And then at random, do any of the same things and get a check engine light. Seems random more than the system doing its job.

Each manufacturer has their own drive cycle parameters for each model they produce. For example on 2002 buicks with a 3.4 liter you have to accelerate to 55-60mph at 3/4 throttle and maintain that speed without going over 60 or under 55mph for 5 minutes if i remember correctly. Im sure someone on here can look up what it is for our cars. Sometimes the car has to be driven a certain amount of miles before the monitor will kick on.

Im a smog tech here in cali and from experience ive seen cars go 500+ miles before setting the cat monitor. Ive also seen the monitor kick on within 5 minutes of driving. It all depends on the car and the parameters. As soon as the monitor sets if it notices anything wrong with the drive cycles that were performed it will throw the check engine light

 

[Performance nut]

Each manufacturer has their own drive cycle parameters for each model they produce. For example on 2002 buicks with a 3.4 liter you have to accelerate to 55-60mph at 3/4 throttle and maintain that speed without going over 60 or under 55mph for 5 minutes if i remember correctly. Im sure someone on here can look up what it is for our cars. Sometimes the car has to be driven a certain amount of miles before the monitor will kick on.

Im a smog tech here in cali and from experience ive seen cars go 500+ miles before setting the cat monitor. Ive also seen the monitor kick on within 5 minutes of driving. It all depends on the car and the parameters. As soon as the monitor sets if it notices anything wrong with the drive cycles that were performed it will throw the check engine light

Ok, I'm with you on this. No I don't know the sequence but I am familiar with the monitors you are talking about. I have been monitoring them with my Kiwi via OBD auto doctor. All the readiness monitors don't clear completely. 7 out of the 8 always clear before I get the check engine light. Surprisingly, the catalytic converter always passes, its the evap monitor that never runs. Is this the monitor that flags the bad catalytic converter?

 

[Randy954]

The evap 99% of the time is always last to set. It also matters how much gas is in the system. As far as the cat monitor setting thats good. At least it recognizes the cat is functioning. Basically how it works is the front 02 sees the exhuast mixture before it hits the cat, the cat is supposed to clean it up but if the rear 02 sees that there isnt a big enough change (cleaning the emissions) then it will tell the computer that the cat is not functioning properly and in turn throw the P0420 code.
Are these cats in the stock location? The further away the cat is downstream the less efficient it will be. You want the cats to get as hot as possible to burn up any emissions. So if theres room to move the cat closer to the headers id move them but if not chances are your either going to have to find a better replacement or just deal with the light. Some tuners can get rid of the light by eliminating the rear 02 but then the monitors for the 02 and cat wont set. If you dont have an emissions check every year you wont even notice but if you do and they check the readiness monitors you will most likely have issues passing.

 

[Performance nut]

The evap 99% of the time is always last to set. It also matters how much gas is in the system. As far as the cat monitor setting thats good. At least it recognizes the cat is functioning. Basically how it works is the front 02 sees the exhuast mixture before it hits the cat, the cat is supposed to clean it up but if the rear 02 sees that there isnt a big enough change (cleaning the emissions) then it will tell the computer that the cat is not functioning properly and in turn throw the P0420 code.
Are these cats in the stock location? The further away the cat is downstream the less efficient it will be. You want the cats to get as hot as possible to burn up any emissions. So if theres room to move the cat closer to the headers id move them but if not chances are your either going to have to find a better replacement or just deal with the light. Some tuners can get rid of the light by eliminating the rear 02 but then the monitors for the 02 and cat wont set. If you dont have an emissions check every year you wont even notice but if you do and they check the readiness monitors you will most likely have issues passing.

Do you know how hot they are supposed to get? Monitor shows they are high 900 to low 1000 depending on how hard I drive it.

As far as stock location, no they are further back. I tried to combat this by coating the headers to see if that would help keep heat in as much as possible.

 

[toplesstripcruiser]

Aren't there tunes that tailor the air/fuel mixture so it won't prodcue as much hydrocarbons, rather than turnoff the O2 sensors?

 

[Randy954]

Do you know how hot they are supposed to get? Monitor shows they are high 900 to low 1000 depending on how hard I drive it.

As far as stock location, no they are further back. I tried to combat this by coating the headers to see if that would help keep heat in as much as possible.

The average cat should get between 800-1500 degrees Fahrenheit depending on driving conditions. Maybe your cats arean't getting hot enough?

 

[Randy954]

Aren't there tunes that tailor the air/fuel mixture so it won't prodcue as much hydrocarbons, rather than turnoff the O2 sensors?

Yes they can tune it out but it would take a badass tuner and a lot of time. I seen a 2006 cammed gto pass the sniffer with no cats. It's really rare but it can be done

 

[2015 Silver GT]

Aren't there tunes that tailor the air/fuel mixture so it won't prodcue as much hydrocarbons, rather than turnoff the O2 sensors?

Yes they can tune it out but it would take a badass tuner and a lot of time. I seen a 2006 cammed gto pass the sniffer with no cats. It's really rare but it can be done

It can be done but it's also highly illegal. Most tuners don't want the risk.

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