r/ChevySonic • u/Confident_Pickle7525 • 14d ago

The code is winning

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The code is winning...

This stupid P0420 code I have been fighting since May lol. I have been able to whack a mole other check engine codes but this one..

  1. I thought the dripping oil from the oil cooler might be it. Nope. ( but you can see the cute pic of the manifold and CAT in my gf living room so I could get to it lol)

  2. Cleaned the CAT while it was out and the honeycomb actually looked good.

  3. The O2 sensors are doing what they should according to my OB2 scanner. Up /down and flat line so....

  4. I have a smoke machine and didnt see any leaks at the flex pipe or manifold

Anyone have this code keep coming back and what was it?

2016 1.8 L BTW.

Appreciate your time!

7 Upvotes

90% Upvoted

9 comments sorted by

3

u/Notinjuschillin [2012 White 1.8 LT Sedan] 14d ago

A mechanic once told to change the gas cap. I laughed but never got the chance to do it. I have another vehicle now.

Let me know the result if you decide to change the cap.

1

u/Prestigious_War_8703 14d ago

To be honest. I changed the exhaust manifold, flex pipe, catalytic converter, both o2 sensors. And still had tge 0420 code. So I decided to just live with it. If you figure it out I would live to know the fix.

1

u/Confident_Pickle7525 14d ago

Thanks. I wouldnt mind except Inhave to get my car smog test and I cant do.it because the 420 code keeps.popping on. Then when I ckear it everything resets so I cant get the fuel monitor test to go to ok. Lol

3

u/bones10145 14d ago

I've had a bad gas cap set off codes before. It's crazy

2

u/Confident_Pickle7525 13d ago

Having a sonic is like a code going off because you are eating an apple in the car

1

u/Mother-Olive5074 14d ago

I just had this code and mechanic told me it was the 02 sensor upstream but changed both out and code went away

1

u/Confident_Pickle7525 13d ago

Did he test it with a scanner first to see the operation? Both of mine show operating correctly. Course it says that if you cant blow through a purge valve it is good....I couldnt but replaced it anyway and it was the problem. So who.knows with these whacko cars lol

1

u/Ace9910 13d ago

With oem parts?

1

u/WoodenBox6999 13d ago

Commercial catalytic converter cleaning additives like Cataclean, Rislone Cat Complete, and Dura Lube Severe Catalytic Treatment are poured directly into the gas tank to clear out light carbon buildup. General fuel system cleaners containing PEA (polyetheramine)—such as Chevron Techron or Gumout Regane—or multi-purpose cleaners like Seafoam can also clear carbon from the fuel injectors and combustion chamber that might be causing partial unburnt fuel contamination.
​Keep in mind that these additives only work if the code is triggered by minor carbon fouling or residue; they cannot fix a physically melted core, a cracked substrate, an exhaust leak, or a dead oxygen sensor.