Engine management system - siemens (all except NAS) (ECM): Description and operation

ECM

The ECM is located in the engine compartment, in the Environmental (E) box behind the battery carrier. A dual connector provides the interface between the ECM and the vehicle wiring.

The E-box is a lidded container that provides a protected environment for the ECM and the EAT ECU. An open hub, centrifugal fan powered by an electric motor ventilates the E-box with air from the passenger compartment. Exhaust air from the E-box is directed back into the passenger compartment. The ventilating and exhaust air is routed between the passenger compartment and the E-box through plastic ducting and corrugated rubber hoses. Operation of the cooling fan is controlled by a thermostatic switch in the E-box. The thermostatic switch receives a power feed while the ignition switch is in position II. If the temperature in the E-box reaches 35 °C the thermostatic switch closes and connects the power feed to the fan, which runs to cool the E-box with air from the passenger compartment. When the temperature in the E-box decreases to 27 °C, the thermostatic switch opens and stops the fan. To prevent the fan seizing up in colder climates, where it may not operate for long periods of time, the fan also receives a power feed direct from the starter circuit so that it runs each time the engine is cranked.

Inputs and Outputs The ECM inputs and outputs are detailed in the Table below: