I recently got 2C39 code, which is Lambda probe in front of catalytic converter, dynamics. It is the only code that appears. I changed new spark plugs first since it due after 45k miles, no luck. I ordered the sensor and replaced bank 1 sensor 1, then the code is gone . After 1 week of driving, engine code popped up again, same code . I'm clueless now. Would anyone shed some light to me . My car is at 115k miles right now.