Originally Posted By: Vikas
NO, it is NOT the post cat O2 sensor.
Aaaaaaaaaaarrrrrrrrrrrrrrggggggggggggggg
The way system functions is that if you put a brand new and better O2 sensor, you will get the P0420 quicker!
When you get P0420, 99% it is because computer has determined that your catalytic converter efficiency is low. Your choices (not all of them are available to you)
1) Factory reprogram to reduce the trip point
2) Clean the catalytic converter (some home made remedies are floating on the internet; use and tell *us* if they work!)
3) Replace with OEM converter. DO NOT BOTHER WITH A CHEAP AFTERMARKET; the code will come back in less than six months
4) Google O2 sensor extension (If anybody asks, you did NOT get it from me!)
Vikas with all due respect you come up with this all the time and it simply isn't always the case.
It is true a older O2 sensor can help resist a 420/430 code but the cat does not have to be defective exclusively to trigger these codes.
I did a cat for a guy last year on a Corolla, he insisted it was the cat and wanted no diagnostics done as it was a waste of money. He got this info from the internet.
Fine. I a had him sign off on this deal "replace cat for PO420 at customer request, no diagnostics".
I replaced it as requested with a brand new OEM unit.
Well he was quite PO'd when the light came back on a few miles later and tried to pass it off on me. "I should have told him it could be something else as i am the mechanic and should know better".
I told him to back back to his internet pals and get a diagnosis and come back and tell me what he want to replace next before tossing him out. lol.
BTW yes it can be a deteriorating (not totally shot) rear O2.
Read this..
http://www.easterncatalytic.com/education/tech-tips/pesky-p0420-codes/
http://www.easterncatalytic.com/education/tech-tips/the-misleading-nature-of-the-po42o-code/
http://www.p0420.com/
http://www.aa1car.com/library/p0420_dtc.htm
Quote:
Sometimes a faulty O2 sensor is not bad enough to set an O2 sensor code but is off just enough to affect the accuracy of the catalyst monitor.
Yes it is more than likely a bad cat but never swap a cat out without fully diagnosing and testing the cat!
Just throwing a cat at a PO420/430 it a mugs game.