What would cause catalyst system efficiency below threshold bank1on a 2002 Monte Carlo ss Had catalytic converter replace 2 weeks ago?
There is a possibility that your O2 sensor is fouled. The O2
sensor is what reads the exhaust air to fuel ratio. Have it
checked..........I would have looked at a bad O2 sensor before i
replaced a catalytic converter. There are some cars with O2 sensors
before and after the cats, and others just have O2 sensors in front
of the cats. I am not sure what you have.