ECU car vs. PCM car vs. ECM in car While ECU, PCM, and ECM are often used interchangeably, there are slight distinctions based on their applications. An ECU typically focuses on engine-related functions, while a PCM integrates additional capabilities for managing the powertrain system. On the other hand, an ECM may encompass broader control over the engine and emission systems in some vehicles. ECUs, PCMs, and ECMs rely on sensors that monitor various parameters such as engine temperature, ...