If your car's ECM (engine control module) is showing signs of failure or problems, it can exhibit several clear-cut symptoms. Usually, a failure or fault with the ECM will light up a check engine light, which you can then use an OBD diagnostics scanner to extract error codes to diagnose it further. Otherwise, you might also experience problems with your car's driveability. For instance, your car might not start, or the engine might misfire and stutter as you're driving along. Other tell-tale signs include feeling a sudden loss of power during acceleration, rough gear changes, or random stalling. Over the long run, other symptoms that could crop up include seeing a gradual drop in fuel economy.