My service engine soon light went on on my 04 g35 6mt yesterday, it has 58k. Checked the codes and got P0420 and P0430 which are catalyst something below threshold bank 1 and bank 2, the previous owner put on hks Hi flow cats about a year ago and never had problems, any help? Ive read this means I need to replace the cats but since both codes came at the same time I was thinking it might be something else

 

Did you ever fix the problem because my car is showing those codes right now to my car is an 04G35X one day my car was sputtering and then you could also feel some blowback from the exhaust. The awd, vdc & slip lights illuminates after clearing the codes, but then it disappears after you restart the car.

I've fixed the problem for both sensors. The CES light is off and I'm good to go so far. The Awd, vdc and slip lights haven't came back on the master cylinder is full. Try replacing the sensors first as a inexpensive alternative and then if the codes clear you don't have to replace the cats, hfcs or test pipes/ what have you.

 

Hi I'm new to this so not sure if I'm posting in the right spot but anyways I have a 2004 Infiniti g35 coupe with the code p0420 and the light inside of the car is (Service Engine Soon) the o2 sensors were checked and one was replaced catalytic converter was professionaly checked a few times oil and filter were both changed along with the air filter and the MAF was cleaned and nothing will solve this problem any ideas??? And also it has been checked for vacuum leaks and none were found.

 

Are you sure they replaced the correct downstream O2 sensor? P0420 is bank1 (passenger side) and they might have mistakenly replaced the driver side one, or they may have replaced one of the upstream O2 sensor. The typical cause would be bad O2 sensor, bad cat, vacuum leaks, exhaust leaks upstream from cat, bad (leaking) injector, test pipes or high-flow cat due to lower exhaust air velocity (bigger pipe + same volume = lower velocity which screws with the downstream O2 sometimes).

I'd take it to another shop if they can't fix it, make sure you find out exactly WHICH O2 sensor they replaced!

https://g35driver.com/forums/attachm...used-banks.png

Bank1Sensor2 is the one with that P0420 error code I think.

NOTE! I might be completely off with the whole driver/passenger side thing, there's a LOT of conflicting info on these forums, some folks say bank1 is driver side, some say bank1 is the passenger side (looking at the motor from the front bumper). I personally have never had this issue so I've never had to VERIFY any of this info!

 

It's my understanding bank 1 is the passenger side and I'm pretty sure that's correct.