Suffering from P0420

Terry1996 · Post by **Terry1996** » 16 Mar 2023, 16:54

Ok, so I took my car to a mechanic today, because I still have the stupid check engine light on. I still have not been able to smog it to put the car in my name. The mechanic is a certified Volvo tech and has been running his shop for almost 32 years. So, I trust his diagnosis. He is saying that the rear cat is bad and needs to be replaced. Now he quoted me almost 6k to have all the cats replaced on the car (that is parts and labor). My car is a 2008 with 228k miles and drives excellently. The interior and exterior are in excellent condition. I am not really sure I want to put the money into the car, but would welcome your opinions on this. Thanks in advance.

Post by **matthew1** » 16 Mar 2023, 17:30

I'd do a stage 0, reset the codes, and see what comes back.

Take a look at this P0420 thread. It's usually the result of "upstream" problems.

Vova585 · Post by **Vova585** » 18 Mar 2023, 23:26

I tend to agree with your mechanic that with your miles you likely need a new catalytic converter. It is great news that your car is running well-meaning your catalytic is not plugged and just lost ability to perform at its finest,but still works. $6k is a lot of money for a lot of people. People that directed you to the 0420 thread were likely suggesting that if you want not to see the check engine light you can try installing nonfouler device($10-20 part) between 2nd O2 sensor and catalytic. It will "officially" make your car good for off road use only and a lot of mechanics will not be willing to do it...but if you have 20minutes and youtube you will be able to help yourself..friend of a friend told me that on his car 0420 is gone for 50k miles...
That's the most likely scenario. However if we are looking at your pending codes your 2nd O2 is reading lean. My question: how that mechanic diagnosed the issue. If he is well trained with modern scanners he can look at fuel trims, o2 performances...but if he is failed to improve with time-it is easy to tell anyone you need 6k in parts and labor. Any chance there is a exhaust leak between front and rear sensor? Also sensor itself might be causing issues. If you will decide you want to keep the car but wait until going all..you can spend $20 as above and wait and see(by yourself a check scanner and erase codes and drive and see what happens). Option 2- replace 2 O2 sensors with OEM or OE from FCP Euro and pay someone to install them(your mechanic will anyway tell you to replace 2 of them upon changing catalytic). And if this option is not helping-you either swap the new sensors into new catalytic or adding $20 device as above...option 3-replace everything and hope that no money light will bother you again..