i disconnect mine all the time do to no cats on my 97. my 3rd o2 picks up no catylist but i got an o2 simulator product to hook up to stop the ce light from kicking on (have no hooked up). it dont even have to be over night i take mine off for 15 minutes then hit the brakes before connecting again to pull rest of left over active current. the only side effects are everything resets in the ecu (air and fuel ratio ect.) its like jumping in a new car. it will take a day for ecu to set in new settings for the way u drive.