See Figures 1, 2, 3 and 4
Fuel injected engines are equipped with the Toyota Computer Control System (TCCS). This integrated control system allows the Power Control System to control other systems as well as the fuel injection. On earlier systems, fuel management is performed by the EFI computer; on later systems, the control unit, known as the Electronic Control Module (ECM) also oversees ignition timing and advance, EGR function and Electronically Controlled Transmission (ECT) functions, as well as on-board diagnostics and back-up (or fail safe) functions.
Unless otherwise indicated, the term ECM will refer to all electronic control modules, including the earlier versions.
The control unit is a sophisticated micro-computer which receives input signals from many sources and locations on the vehicle. It is capable of rapid calculations of many variables and controls several output circuits simultaneously. This system is broken down into 3 major sub-systems: the Fuel System, the Air Induction System and the Electronic Control System.
An electric fuel pump supplies sufficient fuel, under a constant pressure, to the injectors. These injectors allow a metered quantity of fuel into the intake manifold according to signals from the Electronic Control Module (ECM).
The air induction system provides sufficient air for the engine operation. This system includes the throttle body, air intake device and idle control system components.
ELECTRONIC CONTROL SYSTEM
The ECM receives signals regarding changes in engine operating conditions from various sensors. These signals are used to control fuel delivery and other functions. Some of the critical signals used by the ECM are intake air volume, intake air temperature, coolant temperature, engine rpm, acceleration/deceleration and exhaust oxygen content.
ELECTRONIC SPARK ADVANCE (ESA)
The ECM is programmed with data for optimum ignition timing during any and all operating conditions. Using the data provided by the sensors, the microcomputer triggers the spark at precisely the right moment.
IDLE SPEED CONTROL (ISC)
The ECM is programmed with specific engine speed values to respond to different engine engine conditions (coolant temperature, air conditioner on/off, etc). Based on the signals received, the ECM controls the amount of air by passing the throttle at idle. ECM operated voltage output controls either an air valve or ISC valve at the throttle body. By opening or closing the valve electrically, more or less air is allowed into the engine, changing the idle speed.