Engine suddenly lost power, coolant temperature gauge went to zero, and engine cooling fans ran continuously, even though engine was not overheating. engine appeared to be opering in "limp home mode". dealership replaced temperature sensor and problem appeared to be resolved. one week later check engine light came on. dealership performed calibration on new temperature sensor and problem appeared to be resolved. one week later check engine light came on again. dealership replaced temperature sensor and cooling fan assembly and calibrated new temperature sensor.