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Discussion Starter #1 (Edited by Moderator)
Took the car to get smogged today and failed due to permanent p0420 and p0430 codes "Catalyst System Efficiency Below Threshold"
I had the car tuned (2.4 upper, e85, intake, test pipes). It passed smog once with the test pipes. But now, I have to do STAR smog which apparently is more stringent than the normal smog in CA, so I replaced the test pipes with gutted factory cats. No CEL, but the permanent codes were the reason for the fail.

The car sat pretty much all year last year and I did replace the battery. So is it possible that I just need to drive the car more for the monitors to reset and for it to run the test, or will I need to put the factory cats back in and drive it?
 

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I could be wrong, but I don’t think that code will go away unless you can put cats in or perhaps let the secondary sensors ‘think’ the cats are there.

I recall seeing somewhat of a fix, on a Toyota. It involved soldering in a resistor in the signal wire from the rear O2 sensor.


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what are codes set to in the tune? i have a feeling that may be the issue.
 

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In order for the codes to go away the diagnostic for catalyst efficiency has to run and pass. Hallowed out cats will not help and the diagnostics will keep failing. You need cat light off and hallowed cats will not do that. Get some high flow cats and give it a shot.
 

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It'll pass with those codes, after a gazillion drive cycles.
 

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Discussion Starter #7
In order for the codes to go away the diagnostic for catalyst efficiency has to run and pass. Hallowed out cats will not help and the diagnostics will keep failing. You need cat light off and hallowed cats will not do that. Get some high flow cats and give it a shot.
I have a set of factory cats with their insides I can switch out. There is no CEL, since that was turned off in the tune, but I don't know about clearing those permanent codes.
It'll pass with those codes, after a gazillion drive cycles.
Exactly a gazillion?
 

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The best way to do it is put the stock cats back on activate the CEL and let the system do its thing. It will probably need to run and pass 2-3 key cycles before the permanent codes clear on their own. You cant clear permanent codes with a hand scanner or even HP tuners.
 

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It's going to take way more than 2-3 drive cycles to erase a permanent code.
 

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The ECM actually watches the upstream and downstream O2s to see that their behavior correlates. I don't remember the exact sequence, but it involves increasing and decreasing the AFR as the car warms up. Upstream O2s see the raw AFR (which is correlated with what the MAF and MAP say there should be). The downstream O2s are expected to show a reduction in O2 compared to the upstream. So if the Cats aren't there, the test will fail because the front and rear O2s always show the same readings. If the O2s aren't there, the test will fail because no O2 sensors also always show the same readings.

You can thank the Feds for imposing restrictions that make it really hard to circumvent the emissions tests. The fact that the car's systems are actually so robust explains why they don't use a tailpipe sniffer to do an inspection, they rely on the ECM. The only way to pass this is to install Cats, get your inspection sticker, and then remove the Cats until next year.
 

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Discussion Starter #11
The ECM actually watches the upstream and downstream O2s to see that their behavior correlates. I don't remember the exact sequence, but it involves increasing and decreasing the AFR as the car warms up. Upstream O2s see the raw AFR (which is correlated with what the MAF and MAP say there should be). The downstream O2s are expected to show a reduction in O2 compared to the upstream. So if the Cats aren't there, the test will fail because the front and rear O2s always show the same readings. If the O2s aren't there, the test will fail because no O2 sensors also always show the same readings.

You can thank the Feds for imposing restrictions that make it really hard to circumvent the emissions tests. The fact that the car's systems are actually so robust explains why they don't use a tailpipe sniffer to do an inspection, they rely on the ECM. The only way to pass this is to install Cats, get your inspection sticker, and then remove the Cats until next year.
I still have factory cats intact, so I can reinstall them.

Out of curiosity, would the "foolers" that keep the downstream sensor out of the flow work?

What I don't understand is how it passed when I had test pipes, but it failed with gutted cats.
 

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I had permanent codes disappear eventually with a tune and some time.

Couldn’t tell you the exact process though.

To cheat a down stream O2, you jut need to insulate it with steel wool etc in fresh air and let it show the reduction in reading as explained.
 

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Out of curiosity, would the "foolers" that keep the downstream sensor out of the flow work?
I can't honestly say I remember all the details. I had to figure this out on my 02Z06 after I supercharged it. The ECM understands what the Cats are supposed to do. It knows how much O2 is in the exhaust before the Cats. The Cats "catalyze" the oxidation process, without the benefit of flame they get O2 to combine with partially burned and even unburned hydrocarbons in the exhaust. So what comes out the other side of the Cat has to have less O2 than what was going in to the Cat. The ECM varies the mix, intentionally richening and leaning it. It confirms the upstream O2s are working by monitoring the response, and it calculates what the downstream should see and confirms that, too. So a dummy resistive load isn't going to fool the ECM. Like I said, by federal mandate, auto manufacturers have actually made it pretty hard to get around emissions systems. And the proof of how robust those systems are is that State inspections rely on the ECM to say emissions is fine, they don't sniff the tailpipe to see for themselves.
 

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Discussion Starter #14
I can't honestly say I remember all the details. I had to figure this out on my 02Z06 after I supercharged it. The ECM understands what the Cats are supposed to do. It knows how much O2 is in the exhaust before the Cats. The Cats "catalyze" the oxidation process, without the benefit of flame they get O2 to combine with partially burned and even unburned hydrocarbons in the exhaust. So what comes out the other side of the Cat has to have less O2 than what was going in to the Cat. The ECM varies the mix, intentionally richening and leaning it. It confirms the upstream O2s are working by monitoring the response, and it calculates what the downstream should see and confirms that, too. So a dummy resistive load isn't going to fool the ECM. Like I said, by federal mandate, auto manufacturers have actually made it pretty hard to get around emissions systems. And the proof of how robust those systems are is that State inspections rely on the ECM to say emissions is fine, they don't sniff the tailpipe to see for themselves.
I think I'll try a few drive cycles and see if the codes disappear. If worse comes to worse, the cats will have to go back on for a little while.
 

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Discussion Starter #15
According to an unnamed tuner, the cats need to go back on. The tune has the CEL off, because I installed my own parts, the permanent codes are there. I guess there's a magic spell that I didn't use when installing test pipes to keep the codes from showing. Must've been the Harbor Freight magic wand I was using. As usual, I did get some useful advice from members on here.
 
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