2002 Regal Ls OBD code PO420

Eng light is on, my reader says the code is 420. Over the phone the muffler shop told me that it is the converter. I thought it could be a sensor or the converter? He said the sensor is a different code. He said he would replace the converter for $185 plus the sensor for nothing if I supplied the sensor. I thought of buying a downstream sensor and doing it at the same time. Either would cost a lot more if done by my regular repair shop. Does this year have only one converter? Thanks, appreciate your thoughts.

A better scan tool will really help narrow this down. By live monitoring the sensors as the engine warms up. There is only.one converter on this car and an upstream and downstream O2 sensors.

Generally P0420 is the converter. A bad sensor will usually show up as P2A01.

I don't know what your emissions checks and laws are like in your area, but another option you could do is find someone with HP Tuners to tune the code out.

Thanks guys, It gives me a better idea of what to expect. The emissions in AZ are fairly strict. Also most repair shops tend over price in this area. That's why I thought buying a downstream sensor for $60 and getting it installed with the CAT would save me in the long run. If the front 02 was on the way out can it be done later? For the money they want for the sensors I could have bought a much better scanner.

The front o2 sensor can be changed later. Its located near the flange where the downpipe connects to the rear manifold/crossover pipe.

Just change the converter first. No need to worry about the sensors. They are easily replaced later on.

Car is 15 years old......I would replace the sensors, if original.....

Beware of some aftermarket cats.....I have seen cars come in with cats half the size of the original, and the customer wonders why the car is not passing emissions......

Also make sure there is no engine problem taking the cat out.....but chances are, if original cat, it has outlived it's useful lifetime....

That's my intention is to replace the rear sensor and the cat. Thanks' I'll ask about the cat size. Its all original, owned it since new with about 70k miles. It runs good and no other fault codes. I appreciate everyone's advice