Okay, in the process of battling with my service engine light, I finally decided to take my car in to a dealer and have a master Nissan Tech diagnosted my car. It took almost an hour becuase he had to run my car for like 10 mins at 2500 RPM range.

So my questions are: What's the difference between this kind of diagnosis and just reading code off the scan tool? and this time the code is different than my last one, which one should I trust? last time, it was the 02 sensor (bank 1) and this time he said it's the Cat? and he showed me all the graphs he printed out and my car never went into "safe"/limp mode..so that was a relief(btw, mode 5 is a safe mode for maximas??)and mentioned about my O2s are okay???

and how often does Random Tech high flow cat go bad like in half year? He said it's my random Cat, but i told me it's only been on the car for less than 6 months??and when i first put it on, it never gave me any error code. Now it comes to air and fuel mixture problem, since i have CAI, Y-Pipe, etc it make the ECU adjusts the fuel curves, in another words, it put more fuel than stock intake. He said that could have destroyed the Cat due to richer mixture! Oh plus the temperature outside is like 33F according to ECU

So, what should I do now? put back the stock one or get another new Random High Flow Cat, or is something else???
BTW that error code p0420, it only applies to Cali emission cars, so he did not try to re-flash my ECU

Thanks

 

Good question b/c I have the same code, but there is the TSB for the P0420 code. My code started when I installed the Y-pipe and RT CAT. I am not sure what to do either and I am a Federal spec car and the TSB as you mentioned is for Cal emmisions cars. Maybe I will see if the dealership can make the ECU adjustments for my car.

I have also been talking to a super mechanic that cuts himself every time he works on his car and he has an idea that may work, he thinks that the rear O2 sensor is causing the reading and if we take if out so that it does not read the flow then it should be ok, but I have not tried it yet?

 

yeah well Mr "I like to spin on my 60's" it wasn't a big deal just four stiches and my fingertip is still intact!

I'm going to try this on mine tonight. If I don't get a CEL then the front pre-cat is gone! And this should take care of your CEL or you could always go back to the stock cat.

 

Just 4 stiches You make it should like you have had worse working on your car.

NO stock CAT is not good, but that is always an option, hopefully your ghetto trick will work

 

How do you make them to adjust the ECU for you? I doubt they know how to do it!!!!!

I have had Y-Pipe and RT Cat for over 6 months, it didnt' have any problem before until now...damn RT Cat????