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Jay
Jay, Nissan Technician
Category: Nissan
Satisfied Customers: 20371
Experience:  20+yrs experience with Nissan & Infiniti Trained & Certified.Currently still working for Dealer
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2000 Nissan Maxima service engine light on then off without

Resolved Question:

2000 Nissan Maxima service engine light on then off without reset. Code PO403 keeps returning . Replaced center cat conv. under eng. also replaceed main rear cat. conv. within 200 miles service engine light is back on? Any solutions?Many blogs
say the O2 sensors can product false readings,Dealer insisted the conv.needed to be replaced? Thanks Bill Gares
Submitted: 8 years ago.
Category: Nissan
Expert:  Jay replied 8 years ago.
Hello and thank you for using JustAnswer.com

Did you replace the Catt converters with Factory Nissan converters or After Market?

Let me know, Thanks Jay!
Customer: replied 8 years ago.
The cats are from Eastern catalytic. 20yr.s in business and come with a 5yr/50k warranty built to OEM specs. After market and OE or OEM are not same. Thanks Bill
Expert:  Jay replied 8 years ago.
The reason I am asking is cause I have seen after market catt not work properly.

The best way to have the catt checked is to graph the 02 sensors. The front O2 sensors will go up and down, which is the O2 sensor switching rich to lean. Then you want to monitor the rear O2 sensors. If the rear O2 sensors mimic the front and go up and down, then that catt is not functioning properly and that is why you are getting the Catt code. Then it's not a O2 sensor issue either, cause the O2 sensors are doing it's job.

I always check catt efficiency after being replaced and I always check O2 sensor operation. This will ensure the repair was done correctly.

If you have any more questions on this, please feel free to ask. Thanks Jay!
Jay and 2 other Nissan Specialists are ready to help you
Customer: replied 8 years ago.
Okay hopefully my Nissan tech knows how to test/ graft the reading on the cats. Assuming they check out okay where would you look next if the light comes back on? I read that a dirty MAF sensor can produce other codes NOT related to the MAF sensor. Can you outline ALL the steps you would take assuming the next repair does not work. My concern is the car turning into a money pit, I do not want to make repairs based on trial & error. Thanks Bill
Expert:  Jay replied 8 years ago.
Well, as I said. There are a few things I check. First I check what they call the Alfa. This is the air and fuel mixture readings. Then I graph all O2 sensors to check the sensors operations and catt converter function. The MAF sensor if not metering air properly can cause O2 sensors to flat line and not switch properly. So the Alfa should be checked as well. That can effect O2 sensor operation as well. If the MAF sensor is found not metering air properly, then it will need to be replaced. This also should not be replaced with a after market one. I have not seen one work properly yet! There internal resistances don't seem to ever be correct. I have replaced many brand new ones to repair it's function.

If you have any more questions on this, please feel free to ask. Thanks for the Accept. Thanks Jay!
Jay and 2 other Nissan Specialists are ready to help you
Customer: replied 8 years ago.
Thanks