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P0420 SES 01 Nissan Sentra
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bigl
User
Dec 7, 2008, 2:33 PM
Post #1 of 3
(8756 views)
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P0420 SES 01 Nissan Sentra
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Hi, my daughter's SES light went on several weeks ago, it was on for about a week then went off. It has now been back on for the last 2 or 3 weeks. I had the code read at Advanced Auto, the code was P-0420. What is the best and most economical approach to this code? Thanks in advance and have a great Christmas season.
Larry
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DanD
Veteran
/ Moderator
Dec 8, 2008, 11:40 AM
Post #2 of 3
(8745 views)
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Re: P0420 SES 01 Nissan Sentra
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P0420 is set after the computer has performed an efficiency test on the catalytic converter and was found to be below a certain threshold.
This doesn’t necessarily mean that the converter has gone bad; there are a number of things that can cause this code and not having anything to do with the converter.
Vacuum leaks, plugged injectors, leaking injectors, one or both O2 sensors, misfiring spark plug(s), ignition or valve timing and the list goes on and on.
The number of test procedures, likely out number the potential number of causes.
The basic running of the vehicle has to be tested; making sure that it is running as intended and I don’t mean; it seems to run ok, it has to be tested. From there checking that the O2 sensors (pre & post converter) are functioning properly.
Once you have the engine supplying the proper input gases to the converter; a converter efficiency test can be performed, with the use of a gas analyzer.
Taking exhaust readings pre & post converter; you can (with a math formula) calculate the % of efficiency; anything below 70% is considered poor.
There are all kinds of guesses that I could give you but I would likely be more accurate, if I were to write all of the potential causes on strips of paper; put them into a hat and then pull one out.
Diagnosing his type of code would likely be more cost effective by taking it to a person/shop that is familiar with the operations of this vehicle.
No I don’t necessarily mean the dealer; most shops that have stayed up to date should be able to handle this job.
Dan.
Canadian "EH"
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bigl
User
Dec 10, 2008, 4:38 AM
Post #3 of 3
(8724 views)
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Re: P0420 SES 01 Nissan Sentra
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Dan, thank you so much for your thorough reply, that's quite a bit for me to take in, and I'm afraid much of the testing is beyond my capabilities. I will use your info to help me decide where I bring the car. Ironically, yesterday I had the code cleared at a local parts store so I could take the car for its bi-annual state inspection (any type of Check Engine or SES light will mean automatic failure at state inspection) , it passed everything including emissions. Based on that bit of info, are you leaning toward a more probable solution to my problem? Thanks again for your time.
Larry
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