Q&A

 Master

It's really unlikely that if you have a check engine light and have been replacing O2 sensors that you can just reset the computer and clear up the problem. If you have a recurring problem, you may need a better diagnosis of the problem, rather than continuing to replace sensors.

You should check with your dealership, because emission control system components often have an extended mandated warranty, and the dealership will be able to tell you what that warranty is and what it covers.

 Master

Hello Dana,
I have seen vehicles that reprogramming the parameters that the O2 sensor flags a fault code eliminates false illumination of the Check Engine/Service Engine Soon light. Mitsubishi do have a Technical Service Bulletin regarding false illumination of the Check Engine Light Bank 1 Sensor 1, code P0134 affecting 2002 to 2004 Montereos 3.8 Liter engine SOHC. The Bullitain was issued January 2007 TSB# 07-13-001 it deals exactly with the problem you are experiencing. It involves reprogramming the ECU first, then if the light comes back on the sensor may be bad but reprogram first will most likely fix the problem.
I would contact Mitsubishi North America
1-888-MITSU2009. Representatives are available Monday through Friday, 7 a.m. to 4 p.m. (PT) ask for customer service tell them you went to your local dealer, they said they knew nothing of the TSB or reprogramming issue to stop the false illumination of the Check Engine Light and that you were dis-satisfied! You will need your VIN number its on you registration and on the lower driver's side of the windscreen.
I had a similar issue a few years ago. I had worked for a VW dealer, Had a heater core go out behind the dash, I went into the dealer wearing my "street" clothes not my work clothes, they tried to convince me they never saw the problem before and there was no recall. I worked for the dealer the previous year and we were doing recalls on them every second day. I called VW North America and told them what had happened and they covered everything and washed and polished my car.