WARNING: This page is about a different car, the 2019 Nissan NV3500 HD, 2019 Nissan NV2500 HD, and 2019 Nissan NV1500. However, it is still accessible from the selected car via links, so may be relevant.
The ECM consists of a microcomputer and connectors for signal input and output and for power supply. The ECM controls the engine.