A control system for an internal combustion engine includes a fuel injection control system having a first mode, wherein fuel injectors are controlled based on engine condition data supplied by a first group of sensors, and a second mode wherein fuel injectors are controlled based on engine condition data supplied by a second group of sensors. During normal operation of the engine, the control system switches between the first and second control modes based upon an engine operating condition (e.g., engine speed and/or engine load). If one of the sensors of the first group of sensors malfunctions, the control system controls the engine only in accordance with the second control mode. If one of the sensors of the second group of sensors malfunctions, the control system controls the engine only in accordance with the first control mode. In the case of a sensor malfunction in either of the first or second groups, the control system will reduce the engine speed as an alarm to apprise the operator of an engine malfunction.