Q&A

 Rookie

The check engine light was on so I replaced the oxygen sensor and it went out but then days later it came back on so I checked the computer again and then it said converter so I reset it hoping for it being a fluke, it didn't come back on but failed the emissions test and in turn the state turned my light back on so its looking like it may be in my best interest to replace both but I am getting the paperwork to see if it pinpoints which one it is but I am afraid to only replace one just to have the other converter fail later, any thoughts?

Thanks

 Master

Mark,
A lazy or failed Oxygen Sensor/Air Fuel Ratio sensor can lead to a code for a below efficiency catalytic converter. The vehicle's computer uses both Oxygen Sensor/Air Fuel Ratio to monitor the efficiency of the catalytic converter. Some cars only monitor the front catalytic converter, but if the rear O2 sensor is located behind the rear catalytic converter replacing only one catalytic converter may lower your emissions but result in having to change the other catalytic converter in the very near future.
Not all catalytic converter are equal. Many after market catalytic converter are much smaller than the original equipment catalytic converter and may only marginally keep off the Check Engine light. This is particularly true with newer cars!

 Rookie

Thanks, I replaced the sensor at the converter under the car about 2 months ago but not the one by the manifold so I will replace it next, I was told PA will give me a waiver for 1 year if I spend over $150 trying to fix the emissions with no success and that sensor by the manifold I think is over that by itself. At least if that does not cure it I have a year to get the converters replaced.

Thanks

Mark