What is code reader code P0420 mean?

Answer 1

A P0420 diagnostic trouble code is a "generic" fault code that is set when the system sees a drop in converter efficiency.

The problem, in most cases, is an emissions issue, not a performance issue that affects the way the engine runs.

Does this mean the converter has failed and that the vehicle is polluting? Not necessarily, but technically speaking the vehicle is NOT in emissions compliance if it has a code and the Check Engine light is on.

If the Check Engine light is on and you have a P0420 code or any other code, you will FAIL the test -- unless the state allows you to take an alternate tailpipe emissions test to see if your vehicle is actually polluting.

Some states allow this but others do not.

If your state allows an alternate tailpipe test -- and your car passes -- don't worry about the converter code. Your OBD II system may be over-reacting to a perceived emissions problem that does not yet exist.


Source(s):
http://www.aa1car.com/library/p0420_dtc.…