Component Parts: ECM

WARNING: This page is about a different car, the 2017 Nissan Murano. However, it is still accessible from the selected car via links, so may be relevant.

ECM (Engine Control Module) controls the engine.
ECM consists of a microcomputer and connectors for signal input and output and for power supply.

Courtesy of NISSAN NORTH AMERICA, INC.
Battery voltage is supplied to the ECM even when the ignition switch is turned OFF for the ECM memory function of the DTC memory, the air-fuel ratio feedback compensation value memory, the idle air volume learning value memory, etc.