P0420 Trouble Code

[Kendo]

Hello,

I’m looking to buy a 2018 Forest River Forester.

The owner has been open, saying his check engine light is on, and a diagnostic error code reader comes back with a: P0420 Trouble Code (catalytic converter system)

Has anyone ever experienced a P0420 Trouble Code?

What advice can you give to help direct me in resolving this matter?

Thanks in advance for any and all insight, comments and recommendations.

Ken

[jlg2002]

My experience with this code has been

the forward most cat (closest to the engine) is failing and need to be replaced. there are two side on a V configuration engine so budget for both.

[Duckogram]

That could be an elusive code. Many things can cause the computer to throw that one. The range goes from a bad electrical connector to replacing the converter itself. In that range are things like manifold air leaks, bad spark plugs, bad O2 sensor…

The good news is that it does not appear to be fatal. A shop can narrow it down for you. I would suggest paying a shop to do exactly that before you buy it. There may be other codes in memory that could be significant. Also, check the VIN as it may be a 2017 chassis which might make a difference.

Edit: Emission control parts may be covered by warranty. You did not specify Ford, Chevy or MB.

[Kendo]

It's a Ford chassis/engine - 2017

[avengers]

How many miles are on it? Rare to see a cat go bad on a 2017 chassis. Most likely an oxygen sensor or clogged air filter. If it’s been sitting alot open up the filter housing and make sure there are no nests blocking air flow.

Good news is Ford has an 8 year 80k warranty on most of the emissions system including the cat.

[jlg2002]

I hope you others are right. I went down this road on a Nissan Frontier, did everything else stated above (O2 sensors, coils, plugs, checked for lean intake problems, etc...) and still had the problem in the end. Wound up needing to replace both front cats. Instead of laying out the $2K + I traded it in.



My point was to inform you to put that cat replacement cost into your offer for the MH if you decide to go forward with the purchase.

[D W]

I find it hard to believe that a 2017 CAT system has failed already. A number of things need to be checked before pulling the trigger on new CAT. Easy enough to rule out bad CATS. Run the engine for 10 minutes and get it up to operating temperature, then climb underneath with an infrared thermometer. Shoot the inlet of the CAT, record the temp. Then shoot the outlet of the CAT and record that temp. Do this for both CATs. Compare the two readings. The outlet temp should be at least 100 degrees warmer than the inlet temperature. If so, the CATs are fine and your problem is somewhere else. For further diagnosis you will need a scan tool to take a look at the freeze frame data stored with the code. It will give you a picture of all sensor readings when the code was set. Also, take a look at the upstream vs. downstream O2 sensors. The upstream should be low mV and switch constantly RICH-LEAN-RICH-LEAN etc. The downstream should be high in mV and constant. Fuel trim should also be checked.