Engine Control Module: Description and Operation

Deceleration Control System:

The deceleration control (DECEL) system detects engine deceleration judging from the engine speed and the idle switch, and signals a fuel-cut operation to match the engine's needs, based on the coolant temperature and A/C operation. The components of the deceleration system that are computerized engine control system related are the engine control unit (ECU), throttle sensor, water thermosensor, brake light switch, A/C switch, water thermoswitch, and neutral/clutch switch (M/T only).
The ECU receives inputs from the sensors and cuts the fuel injection signal to the injectors. The throttle sensor is a potentiometer splined to the throttle shaft. The potentiometer rotates with the shaft as the throttle plates open and close. The varying resistance of the potentiometer alters the reference voltage emitted from the engine control unit (ECU) and creates a signal for use as input by the ECU. Incorporated into the throttle sensor is an idle switch. The idle switch detects when the throttle valves are closed and sends a signal to the ECU. The water thermosensor detects the engine coolant temperature and sends a signal to the ECU. The brake light switch detects braking operation (deceleration) and sends a signal to the engine control unit. The A/C switch detects A/C operation and sends a signal to the ECU. The water thermoswitch detects radiator coolant temperature and sends a signal to the engine control unit. The neutral and clutch switches detect when the vehicle is in gear and the clutch is engaged. These switches send signals to the ECU.