I have a 2000 model M6 TA which has been having trouble getting rid of a P0420 code. The car has factory cats on it which passed smog according the previous owner. He also gave me another set of cats that were on the car when he bought it two years ago. He never had it smogged with those cats but I decided to try the driver's side cat anyway to see if it would fix the issue. My exhaust guy told me the replacement cat is certified for use in California, but the car still set a CEL about 30 miles later. After performing a whole battery of tests related to the code, I have determined that all four O2s are good and it is actually the catalytic converter itself. I also discovered that bank 1 was slightly LEANER than bank 2 due to loose intake and exhaust bolts, but all that is fixed now and it's definitely the cat that needs replacement. STFT and LTFT are almost identical on both banks now.

Now my question is, just for the purposes of passing smog, is it possible to extend the bank 2 sensor 2 output over to bank 1 connector? Or would this fail during a visual or functional test?

 

It would likely fail if they can see the wires. They typically stick a mirror under for the inspection of the cats and 02's

 

So I found this too. Seems rather extreme but I do have a bad O2 sensor laying around to experiment with.

If you remove a rear oxygen sensor and pack it with red RTV silicone, that will destroy the oxygen sensor in a way that will trick your car's computer into thinking the catalyst is okay. The sensor will not work well enough to report that extra oxygen is coming out of the converter, but it will still generate enough voltage to pass the car's oxygen sensor activity test. Never do this to a front oxygen sensor because it will mess up the fuel system.

Well there it is, one of the best kept secrets in the smog-loving world. This works nearly 100% of the time. You will never find a mechanic that will do this for you, so you had best be prepared to remove that sensor yourself and put it back in.

Certain newer cars will not tolerate having the rear oxygen sensor dummied up, so you will have to get a new sensor after passing, or the car will start to underfuel and you will get a code for "fuel trim rich."

However, I believe this would set a rear O2 sensor code when the PCM sees that it isn't reporting a rich condition when it should. Does that sound right?

Then here's my original idea in the same author's words:

Another mechanic sent this other converter trick to me, and I tested it today and it did work.

Let's say you have a car with two converters and four sensors. If only one of the converters has failed, you can sometimes connect both rear sensor signal wires together and the average of the two makes both look good in the eyes of the PCM (Powertrain Control Module).

Today I had a 2001 Sentra with four sensors even though it was just a four cylinder. The car had a P0430 error message for the Bank Two converter only. The rear oxygen sensor wire connectors were right next to each other under the hood, so I just jumpered the two signal wires together and ran the drive cycle. Problem gone.

If one gets creative at the PCM connector, it wouldn't show up in the visual test. However, would the voltage reported to the PCM really be an average of the two sensors?

I found all this crap at https://axleaddict.com/auto-repair/Catalytic-Converters-For-Dummies in case anyone is interested.

 

99+ cars in Kalifornia are e-test only now, plus the visual. I just disabled all the codes in the PCM and passed SMOG with no problems.

 

I am aware 99+ are e-test only but I thought the smog station would know if any codes were disabled.

On a related note, evidently an RC low pass filter on the O2 sensor will slow down the oscillation and trick the PCM into thinking the cat is OK. That's probably going to be a cheaper fix for now but I've really got to invest in a cable and HPtuners down the road.

 

you can buy an o2 simulator for tjhe rear cats and no codes will show. it just does a square wave .1-.9 volts pattern. cant be more that $30

 

You can also use a spark plug fouler as it pulls the 02 sensor out of the direct stream.

 

Yes I thought about that earlier but I was under the impression that any electronic trickery might get detected. The RC low pass filter worked for a short while but the code came back because the fix doesn't fool the oxygen storage test. However, I replaced the post cat O2 with a bum sensor I had laying around that was switching too slow and not generating enough voltage, which is ironically exactly what is needed to show that the cat is good. Just checked the monitors yesterday and catalyst shows ready to go!

I didn't want to go this route as I don't have access to a drill and tap and die set for rethreading the fouler.