P0420: bad pre-cat or the main catalytic converter

[Kedar Patwardhan]

I am looking for some expert help and guidance. I have a 2005 Maxima that gave a P0420 error some 4 weeks ago. It also gave a P1800 error. I checked the VIAS system, removed and cleaned the sensor plug and gave it a try. The solenoid engaged as the engine rpm went above 3000 rpm. So reset the errors and drive the car around for a few days and the SES light remain off and the P0420 was gone too !
Then a few days ago, the P0420 is back but the car is not at all sluggish to drive. The mileage is around 17 mpg in city traffic which I suppose is normal for a Nissan Maxima.

So back to the P0420, is there a way to confirm that the catalytic converter is bad and not the pre-cat ?

Topic

[Rob]

ya a 5 gas exhaust gas analyzer… could tell you better… but only shops have them they are like $1k
http://www.obd-codes.com/p0420
gives some ideas of test to check

[Kedar Patwardhan]

Thanks Rob. I will pass buying the exhaust gas analyzer 🙂
But I will report back on the O2 sensor fluctuation (pre cat and post cat).
Thanks again !

[pilotvp]

I had this P0420 code, and I removed the CAT to inspect the sub-strait, then I back flushed the CAT with degreaser, you can soak it in soapy water over night too, followed by back flushing with water. Reinstalled the CAT with no codes. Started using Shell gas too!

[guess it begins with R and ends with n]

the 3.5 L maxima? I have the 01 3.0L and I had to remove the air intake. I replaced the knock sensor and water outlet nipple seal+hose.

The knock sensors goes then the car can’t re adjust after it misfires. Have you checked the Knock sensor? You need to test it in the mega ohms slot.
The fuel injectors have screens inside them that clog up and go bad too. I’m going to push carb cleaner through mine and jump off the injectors to clean them out before re installing them.

I think I had some leaky fuel injectors because the clips were kind of dirty with gum build up on them.
depending on how many miles the engine gets striped down to the valves and crankshaft. the timing chain gets replaced and engine gets re sealed. Does this sound right? In the process all the hard to get to sensors and tubes have to be replaced. What’s your views Eric?

[Paul Hartmann]

I had a code like this on my son’s camry. sucked seafoam into the intake, let it sit 5-10, and then drove it in second gear. bye, bye cat. code

[guess it begins with R and ends with n]

Have you checked the fuel pressure ? I’d say also these fuel pressure regulators could become faulty. I found an injector in my 01 to have been sticking open causing all kinds of issues.

[Author]

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