P0420

[Mattp10]

I had a slight miss before my 125k service on a 2015 vf commodore 3L v6. The spark plugs were replaced the next day a check engine light came on. Got it scanned and says the p0420 Had it looked at by an exhaust shop and they said it’s fine. Swapped coil and the 4 c02 sensors still have a miss with the car warms up and the error code keeps coming up any idea?

 

[Lex]

Just googled your error code. Catalytic converter? Hope it helps?

p0420 - Google Search

 

[Mattp10]

Just googled your error code. Catalytic converter? Hope it helps?

http://[URL]https://www.google.com/search?client=opera&q=p0420

[/URL]

Well thanks captain obvious I mean does anyone know what it is I have been told my cat is fine

 

[Skylarking]

Loss of cat efficiency can be caused by faulty O2 sensors (cat is ok), exhaust leaks (cat can’t work well), or damaged cat converter (impacts break ceramic core, oil or coolant leaks into exhaust or some non cat safe RTV sealants coat ceramic core so it won’t work). Injectors can also cause issues if not working as they should...

A working cat will have a temperature difference between the converters front inlet pipe and the rear outlet pipe. Note sure if the rear should be cooler than the front?

A quick Google search would have found such rather quickly but if googling isn’t easy for you, here’s just one video for you to view

 

[Cfb_rolley]

Usually this error pops up with aftermarket cats/exhaust systems. I had it when I had my system installed, did a bit of investigation and found that the downstream O2 sensors were fouled shitless. problem solved by cleaning them up and using an 02 sensor spacer to move them out of the direct exhaust gas stream, but this is more of a band-aid fix and a tune is needed as I still get the slight miss that you're describing too.

In your case, (I'm assuming factory exhaust) you've already replaced the 02 sensors, so I'd say it's either something along the lines of what Skylark pointed to, or there's something going on that's causing the 02 sensors to foul up pretty quickly, so the root cause could even be related to wrong plugs, dirty/faulty MAF etc. causing it to run a bit rich.

 

[Ron Burgundy]

Well thanks captain obvious I mean does anyone know what it is I have been told my cat is fine

Did they actually remove cats and inspected them captain ?