2003 Other Jeep Models Engine Light

I have a 2003 Jeep Grand Cherokee that runs well. However, the engine light has been on for some time now. My son, who is a Ford certified mechanic said that the code calls it an Oxygen Sensor issue, he replaced the three oxygen sensors, but the light will not go off. However, there is a dispute between my husband and him regarding the fact that he spliced some wires to install one of the sensors He used the Jeep manual for the wiring. Since the light still won't turn off, he thinks I may have a processor problem and should probably take to a Jeep dealer for a costly repair. Any suggestions?

Thanks!