Hello,
I have replaced the cat about 4 months ago and O2 sensor, recently replaced the fuel pump and now it’s pulling the P0420 code. I’ve put more money than it’s worth into this car and I’m not willing to replace the cat again. I JUST replaced the cat so what is the possibility this is the cat again? Is there something I can do to fix this?
It is a 2016 nissan versa note S, taking note so show my husband! Thank you! It has around 100k miles
Please tell him this:
On a 7 year old car it is unlikely the CAT or Sensors are faulty and need replacing. Unless there has been some serious neglect and damage.
Some of the most common reasons for P0420 are when the exhaust system after the CAT but before the lambda sensor has leaks from damage or corrosion which lead to air leaking in and upsetting the O2 sensor.
Get eye protection and a spray bottle and spray it with dish soap and water and look for bubbles where the exhaust has leaks.
Exhaust leaks can be repaired by an exhaust repair kit, often using high temperature sealants and clamping or tying metal sheets over the holes.
Another common reason is when ignition plugs or coils fail. Spark plugs are usually rated to well over 50k miles if they are iridium but you should check them.
Ignition coils will cause the engine to either misfire or not properly ignite which will lead to the code. It may be difficult to identify which plug is failing without an error code.
Everything mentioned here are not expensive to purchase and isn’t too difficult of a job to do.