Reader Question: I have had both my O2 sensors and my catalytic converter replaced over the course of the last year and a half on my 1998 GMC Sonoma (2.2 Liter), with the converter being first. I have failed my emissions test due to a 0420 code from my OBD.
What exactly does a 0420 code mean? Is there a way to determine if the problem is related to the converter or the sensors without taking it to a mechanic? I am trying to avoid the diagnostic fee, which is additional, not included within repair costs.
My emissions are due in February and I work out of town extensively.
That code 0420 is for a catalytic converter problem. If the check engine light has recently come on (since you replaced the converter), I would suspect there is a problem with the converter.
Do you have a warranty on the converter? If you do, I would go back to the shop that installed it and have them test the converter and I hope they will do so under warranty. I do not know of a test or trick that you can do yourself to test the converter.
I use a local muffler shop in my area to replace converters on customers’ vehicles. I usually pay between $125 and $200 for the converter and installation of an after market (non-GM) converter.