After changing radiator the check engine light stays on.

The radiator is most likely a Direct Ozone Reduction radiator. There is a sensor that is incorporated with the original radiator. When the sensor is removed,a tamper code sends a signal and the check engine light stays on, making it impossible to have it smogged. From the research I have done, Mitsubishi has no one to make this type of radiator and finding one is almost impossible. Some say this radiator will not be available until May and is over $500.00! I would suggest complaining to Mitsubishi regarding this problem and have them come up with a solution to defeat the code and make it easier to replace the sensor and radiator separately.