I have a 2007 G6 GT and my problems all started with the left front catalytic converter. Dealers said an after market won’t work because it won’t give the correct emissions reading. I live in Pa. But a new one is $650 and up. So I went with after market. Now check engine light is on. Front O2 sensor. Found out it was unplugged. So I plugged it in. Now service traction message pops up. Transmission shifts like a sledge hammer is being used. So I unplugged the O2 sensor. Everything back to normal. Except check engine light. So I replaced the O2 sensor. Plugged it in and all. Check engine light still on. Something about lean fuel #2. Service traction message pops back on. Transmission slams into gear again. So I unplugged the NEW O2 sensor. And everything back to normal. Except check engine light. ANYONE.....have ANY clue??? It’s a 3.5 ltr. Only 88,500 miles. I love this car and don’t wanna have to blow it up!!!!