chief472

One of the first things someone should always check with a P0420 error code, is the MAF (mass air flow) sensor and the air filter. The MAF gets dirty and needs to be cleaned with MAF sensor cleaner or an electronic cleaner. I usually use a q-tip also. If the MAF is dirty with a dirty air filter it will often cause a P0420 code to be set. Its a lot cheaper, to clean the MAF and check the air filter, before proceding to checking a CAT or O2 sensor.