Got a question for you all. I have a cold air intake on my 96 5.0L and I keep getting the p0420 code. I heard it had to do with your engine leaning out. Just wondering if I should put my stock air system back I. For the winter.

Thanks,
Jayden

 

P0420 means that the engine could be running lean because of a bad oxygen sensor or you have a leaking exhaust manifold or bad catalytic converter.

I have a custom air intake on mine Ive had for a while and it wont throw that code. Try checking your exhaust and Inspect the sensors see if that gives you anything. Its possible it could be the heated oxygen sensor in the exhaust manifold. Also your coolant temp sensor may be bad or going bad if you're having issues with that.

(Edit) But then again that code alone usually should mean that they are all working properly to pass good with the PCM before trying the PO420 test, who knows.

 

Wow what are the odds. I just pulled this same code tonight on my 2001 Trans Am. Glad to know what it is. I'll try and clean the O2 sensors first.

 

It means you've got a bad catalytic converter. I didn't want to spend money on my 10 year old truck on a new converter, so I tried this $5 solution and it worked! Took more time going and buying the defoulers than the work to get it installed. Oh yeah, rent the o2 sensor removal tool when you're buying the defoulers. It's the downstream O2 sensor by the converter. Several thousand miles and still no check engine light: