The Reduced Engine Power warning light can pop up due to various causes. But in the case of the Malibu, the most common cause is a faulty Throttle Position Sensor or TPS. If the sensor goes faulty, the car's Engine Control Unit will go into panic mode and limits engine power to minimize damage. Replacing either the TPS or the throttle body assembly should fix the problem. You can also diagnose it first by using an OBD-2 scanner to find the trouble codes.