P0420 code (1 Viewer)

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So my CEL came on throwing a P0420 code on bank 1!

I've changed the downstream 02 sensor previously but not the upstream sensor.
What's the chance it's the sensor and not the cat?

Thanks cruisers
 
So my CEL came on throwing a P0420 code on bank 1!

I've changed the downstream 02 sensor previously but not the upstream sensor.
What's the chance it's the sensor and not the cat?

Thanks cruisers

A very good chance it's the oxygen sensor or an air leak. Visually inspect to see if you have holes in your exhaust and replace the oxygen sensor.

Try this thread:

 
A very good chance it's the oxygen sensor or an air leak. Visually inspect to see if you have holes in your exhaust and replace the oxygen sensor.

Try this thread:




Just another thing to mention is the steel flexi is leaking!
 
Could certainly be adding to the problem, or be the problem.
 
When I had this code it was due to my o2 sensor coming unplugged. So always worth double checking the connection, which I did not do until I crawled under with new o2 sensors in hand....
 
had small leak on Y-pipe.
Have truck cold. Get someone to start it up and run hands down from header, y-pipe towards cat and see if you can feel air being pushed out. You've only got a few mins before it gets toooo hot!

PS still have leak. Tried various "putty" exhaust fixes but always blow out after a few days. I just reset code until I get around to a full SS exhaust replacement (from Aussie) - with new headers
 
So just an update so far..
I cut the steel flexi off and put a new one on which immediately sounds much better as its not leaking!
Went wheelin and drove to work 2 days and the code hasn't come back yet!
Fingers crossed!!
 

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