powertrain control module (PCM) May have same functions as the ECM, but may also control the transmission and anti-lock braking systems. 2 light control module (LCM) May operate warning systems, turn signals, and the horn in addition to its main function of controlling interior and exterior illumination. 3 restraint control module (RCM) May have same functions as a GEM and LCM, but may also be the vehicle's communication network for all the modules. 4 transmission control module (TCM) Regulates shift point for peak efficiency and performance. 5 body control module (BCM) May operate warning systems, turn signals, and the horn in addition to its main function of controlling interior and exterior illumination