Grounded O2 sensors possible bad ECM

My son bought a 2009 Jeep Wrangler JK a few years ago (long story but got totally scammed). Failed emissions in CT and can't get the engine light off so they will not retest. So, now it can't be registered without passing emissions. I took it to a mechanic and the dealership had grounded all the O2 sensors to the wiring harness. He also pointed out a ground wire under the hood that should not be there. At this point, I just want to get the engine light off and hopefully pass emissions so I can register and be good for a few more years. Also, the mechanic said there is really nothing else they can do to troubleshoot the issue because of all the "grounding" to bypass the original problem. Any suggestions or is this just a big expensive lawn ornament now?