My catalytic converter failed at roughly 70k miles (confirmed by mechanic and replaced). I have now been having transmission issues ever since, starting with the rpms jumping up on their own when trying to downshift (reproduced by mechanic) and ending with the car fully going into limp mode while in the middle of driving on the highway at speed. The former never triggered a light or produced codes, and with the latter the CEL flashed three times at the very start of the breakdown, and then went off and never came back on, despite the obvious problems the car was having.