Oh. You must really know what you are talking about, then.


Can you show us a third party passage that would support this position? All electronic diagnostic systems rely on sensors to provide facts, which are used to interpret the truth about what is going on. In order for a DTC to be absolutely correct, the related sensors must always report correctly. While I am not aware of ANY sensor that performs 100% reliably, I have linked information directly from a reputable sensor manufacturer (above) that indicates how O2 sensors can become contaminated and report erroneously. Can you show us how the Wells Counterpoint article is incorrect?


No one in this thread has recommended replacing any sensors. The recommendation was to switch them to confirm their proper operation before making any large investment.


So.... what's your expert advice for the OP? Are you recommending that they go straight to a professional and throw down money for a new CAT with no other investigation required? Should they take the advice of the first professional they saw and replace both?

 

Just to clarify things, if you remove or gut the cats but install o2 sensors, will it throw the check engine light?

 

i have read that if you space the rear o2's out with a spark plug anti-fouler it wont set the ses on gutted cats

for the money your guy wants id buy long tubes with catted y pipe..

really you can just buy the 99$ magnaflow cats and weld them in there, i run them on my car and it passes emissions with flying colors.

 

Yes.

This works, but not in all cases. Old Ford spark plugs have the same thread as O2 sensors. You stack both anti-foulers (2 per pack) with one drilled to accept the sensor. Essentially all it does is remove the sensor from the exhaust stream and heavily shrouds it, changing the sampling. Most PCMs can be tricked into a higher efficiency calculation (P0420/P0430 will not be triggered) using this method. It works well where aftermarket converters are used and are near the efficiency threshold. All aftermarket converters lack the proper catalyzing metals, which is why they are cheaper than OEM.

 

The OP mentioned living in Oregon. Does Oregon have a sniffer test? If not, this problem can be bypassed with O2 sims or custom tuning to disable the P0420/430.

These codes are tripped when rear O2 values too closely (and too quickly) match front O2 values, indicating a reduced oxygen storage capacity of the cat and thus increased tail pipe emissions. This doesn't really matter unless you have to take a sniffer. O2 sims/custom tuning will make it possibile to pass an OBD scan test, same as if you had a ORY.

 

Thanks everyone for the answers! I got the cat installed and I'm having a problem. The car is making a grinding noise when I turn left or when I'm in drive at a light. It sounds like gears grinding but it wasn't doing that before the install. Also when I push on the gas is makes slight rattle(ish) sound and when I tested it without the muffler (which sounded amazing) it didn't make the noise. Any help again is much appreciated guys!

 

Inspect the exhaust repairs. What you're describing sounds like the exhaust is contacting something it should not.

 

yes, it can, and the only thing that monitors the cats are the rear o2's, so, read up a little. What sensor do you think would report the poor efficiency of the exhaust gas exiting the catalyst?

Source: ASE Master Technician with L1 Cert, Nissan Master Technician, GM Specialist Technician.

 

This is a bit misleading. Yes, rear O2 vaules are evaluated by the PCM as a condition for setting P0430/420, but rear sensor values alone aren't what triggers the MIL; what the PCM is looking at is the relationship between the front and rear O2 sensor readings when those DTCs are run. So it would be correct to say that input from both the front and rear O2s play an equally important role in the monitoring of catalyst efficiency - not just the rears.

Source:

North American Operations
General Motors Corporation
Warren, Michigan 48090

GM Service Manual, F-Platform, Volume 2 of 3, GMP/00-F-2, Engine Controls - 5.7L page 6-1629:

"The PCM measures the time it takes the rear HO2S voltage to cross a reference rich/lean threshold minus the time it takes the front HO2S voltage to cross the same rich/lean threshold. The time difference from the front and rear HO2S is the oxygen storage capacity of the catalyst. This DTC sets if the time exceeds a predetermined threshold."

 

So... Are you an OCB or parts replacer?

 

based off everything you've said, there's no room for you to speak "Mr. Meineke." you stated the rear o2's will not set a 420 or 30 code, yet, go ahead and take em out and see how well the cats are monitored. Sorry pal, you don't get through any manufacturers line of training simply by throwing parts at anything. Obviously a quick check of the rear O2's in relation to the fronts would be in order, as well as seeing if they respond to either a power balance test or an increase or decrease of injector pulse width. But, in my experience, 95% of the time, these test will point all fingers at the cat on the bank that correlates to the code.

 

In context... I stated that a faulty downstream O2 sensor CANNOT set a catalyst inefficiency DTC.

Removing a sensor? That is completely irrelevant to the topic, and it's clear you don't even know why.

And not only can you be manufacturer trained and certified by replacing parts (there are a few in every shop I've ever been at), it seems that you can also obtain it without a clear understanding of powertrain control, like you.

 

false, you said oxygen sensors CANNOT trigger a catalyst efficiency code. So, the fact that the only thing monitoring the cats are the O2's, and in turn, are the only sensors responsible for triggering those codes, then you obviously dont know jack **** about diagnosing powertrain management. I think we all see that here.

Now, based off your original post in this thread which is quoted above, in which you state that "Oxygen Sensors Cannot Trigger a Catalyst Inefficiency DTC", Youre implying that it is not the job of the O2 sensor to monitor the Cat and relay the info back to the PCM for evaluation and comparison with front O2. But check this out, it is the official description of how everything is monitored...straight from GM. (P0420 code listed)


In order to maintain a reasonably low emissions of Hydrocarbons (HC) Carbon Monoxide (CO), and Oxides of Nitrogen (NOx), a three-way catalytic converter is used. The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas. This reaction converts them into harmless water vapor and carbon monoxide. The catalyst also reduces NOx, convening it to nitrogen. The PCM has the capability to monitor this process using Bank 1 HO2S #2. Bank 1 HO2S #2, located in the exhaust stream past the three-way catalytic converter, produces an output signal which indicates the oxygen storage capacity of the catalyst. This determines the catalysts ability to convert exhaust emissions effectively. If the catalyst is functioning correctly, the Bank 1 HO2S #2 signal will be far less active than that produced by Bank 1 HO2S #1. If a problem exists which causes the PCM to detect excessive Bank 1 HO2S #2 activity outside of an acceptable range for an extended period of time, the PCM will set DTC P0420. This indicates that the three-way catalytic converters oxygen storage capacity is below a threshold considered acceptable.

So, to say an Oxygen Sensor cant trigger the code is wrong, as it is one of the inputs that the PCM uses to monitor Catalyst Efficiency. When you went ahead and tried to revise what you originally said to a FAULTY DOWNSTREAM sensor, that would be correct, as it would most likely throw a performance or no response code. It'd be great if every time we were wrong, we could change our stories to make ourselves right, but thats not how it works pal.

So you're telling all of us here the if the rear O2's were completely deleted from the picture/circuit, then the PCM could still somehow monitor Catalyst? Must be some of that automotive PFM at work (Pure ******* Magic).

And by the way, insulting someone's profession based off of a little internet debate, is not really what this forum is about. It's about helping people with problems. If that's what we're doing, then I'm sure Job Hopping through "All The Shops You've Worked At" has really moved you up the ladder in the Automotive Industry.

Just take a peek at the general consensus of everyone that has replied to your posts....this thread speaks for itself in regards to your information provided.

 

I think this thread has gone well past it's service life. Time for retirement....