# P0420 code can’t get rid of.



## CRUISE-CRUZE (Nov 8, 2010)

Welcome aboard!
Try to reset the code and use a couple full tanks premium gasoline 93 grade. In winter time the quality of gasoline may be lower than the number posted.


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## GMDONE (Oct 15, 2019)

Garcia said:


> I’ve had the P0420 code and I’ve looked up and tried everything there is to do to fix it. It has a new catalytic converter, both o2 sensors new, new oil, new spark plugs and coil pack, new gasket for exhaust manifold and CAT, and new coolant temp sensors but the code just keeps coming back and at this point I am out of ideas. Any idea on what else could be the problem? (2011 Chevy Cruze LT 1.4T)


Catalyst inefficiency generic code. Can also be a vacuum leak in the manifold still. How did you end up replacing the cat? A shop tell you it was bad along with all the other components?


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## Garcia (Dec 17, 2019)

I’m a military mechanic. Notice the cat was getting bad when I started smelling that rotten egg smell code went away for maybe 2 days and came back. And I have a scan tool that gave out possible solutions along with research related to the code. Today started it up before going to work and I noticed the car shaking but couldn’t tell where it was coming from but I believe it was the exhaust pipe and there was also some popping sound like it wanted to shut off I just pressed the gas a few times and it stopped.


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## Blasirl (Mar 31, 2015)

A code P0420 may mean that one or more of the following has happened: 

Leaded fuel was used where unleaded was called for (unlikely) 
A damaged or failed oxygen / O2 sensor 
Downstream oxygen sensor (HO2S) wiring damaged or connected improperly 
The engine coolant temperature sensor is not working properly 
Damaged or leaking exhaust manifold / catalytic converter / muffler / exhaust pipe 
Failed or underperforming catalytic converter (likely) 
Retarded spark timing 
The oxygen sensors in front and behind the converter are reporting too similar of readings 
Leaking fuel injector or high fuel pressure 
Cylinder misfire 
Oil contamination
Read more at: P0420 Catalyst System Efficiency Below Threshold

*2011-2016 Cruze 1.4 PCV Valve Cover/Intake Manifold Issues*


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## solar0329 (Mar 14, 2020)

Garcia said:


> I’m a military mechanic. Notice the cat was getting bad when I started smelling that rotten egg smell code went away for maybe 2 days and came back. And I have a scan tool that gave out possible solutions along with research related to the code. Today started it up before going to work and I noticed the car shaking but couldn’t tell where it was coming from but I believe it was the exhaust pipe and there was also some popping sound like it wanted to shut off I just pressed the gas a few times and it stopped.


The rough running and popping makes it seem like a vacuum issue. When the car is running, can you hear a hissing sound under the hood?


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## January (Oct 2, 2019)

Garcia said:


> I’ve had the P0420 code and I’ve looked up and tried everything there is to do to fix it. It has a new catalytic converter, both o2 sensors new, new oil, new spark plugs and coil pack, new gasket for exhaust manifold and CAT, and new coolant temp sensors but the code just keeps coming back and at this point I am out of ideas. Any idea on what else could be the problem? (2011 Chevy Cruze LT 1.4T)


 Did you ever find out what the issue was? my car is doing the same.


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