FIrst, if the front O2 sensor is working properly the car is not running rich.
The O2 sensor has the final say and will bring the mixture to hover around stoichiometric when in closed loop.
The computer is compensating for the difference between what the fuel map expects and what the O2 sensor indicates.
As long as the trim is less than 25% the check engine light will not come on; you should drive on and not worry about it.
If the engine runs strong, gas mileage is good, no check engine light, then the O2 sensors are okay, so again, drive on.
The O2 sensor has the final say and will bring the mixture to hover around stoichiometric when in closed loop.
The computer is compensating for the difference between what the fuel map expects and what the O2 sensor indicates.
As long as the trim is less than 25% the check engine light will not come on; you should drive on and not worry about it.
If the engine runs strong, gas mileage is good, no check engine light, then the O2 sensors are okay, so again, drive on.