0420 not good times

stainless

stainless

New member
I have a cel that is reading p0420 when i reset it my engine starts to run at low rpms at idle 750 or almost stall. I have replace the orange upstreem 02 sensor but i still get the code. About 90k 06 foz x . Should i swap out the rear/ downstream? Both are a bugger to remove and i still have most of the front off at this point. image.jpgimage.jpgimage.jpg

 
Could be an exhaust leak, bad catalytic converter, or secondary o2 sensor.  Most likely guesses anyway.

The car will run crappy after you reset codes because all of the ECU's learned values are reset, and it operates in a 1/2 timing advance mode until it knows things won't blow up.  Totally normal.

 
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I had the p0420 when my exhaust flange gasket rotted out and the exhaust leak was bad enough to throw the code.

 
Sounds like i should let the dealerships techs take a look. I am just a bit peeved because it started soon after i got my car back from having head gasket repair...groan.

 
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Well they do have to pull the exhaust to do that so it's certainly possible they didn't tighten it down enough or a gasket isn't in right.

 
If it's a cat they could be still under warranty cause I think they are covered till 150k miles if I remember correctly

 
pzev california emissions car will be covered if you put it all back together and make it look like you haven't touched anything. 

why did you take the bumper off?

Low idle and stalling is just the ECM trying to relearn the idle.  It will be dumb until it runs thru a couple fan cycles.  Everytime you clear the memory you have to let it idle for 45 minutes until it learns how to idle or it will stall while driving 1,000 times.

Do not bring to the dealer until the code comes back.  It will come back.

 
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inski said:
why did you take the bumper off?
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Maybe he thought it was an audi 
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Upstream sensor was behind the radiator, had to use a breaker bar on the wrench to get it off. Inski you work in auburn? So i may have fixed it? The car is running ok now.

 
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stainless said:
Upstream sensor was behind the radiator, had to use a breaker bar on the wrench to get it off. Inski you work in auburn? So i may have fixed it? The car is running ok now.
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Just got my car back from getting a new engine and now its throwing this code. I feel your pain. Let me know what ends up working for you. 

 
yup, in Auburn, for now.
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Hopefully the code doesn't come back, if it does make an appnt at Evergreen.  They can run your VIN and see if its covered.

Abby, your car is not a PZEV.  Most likely not covered.  If you're in Cumberland county you'll probably need a new cat.  If not in Cumberland County just run it unless it acts like it's clogged, then replace it.

 
Fyi, it's easier to drop the headers to get at that sensor, especially if they've been off r recently

 
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