What Does Code U0100 Mean? U0100 stands for “Lost Communication with ECM/PCM.” The Engine Control Module (ECM) is the computer responsible for controlling the engine. The ECM communicates with other ...

The Engine Control Module, or ECM, directly controls the engine. Still, it can’t do that properly without the Transmission Control Module or TCM and PCM, which work together and exchange information.

If you've had to have your car serviced or had a trouble code read, you may have heard about the PCM, but what does the module do for your car?