Computers and Control Systems: Description and Operation

EFI System:

The Toyota Computer Control System (TCCS) is the central control for electronic fuel injection (EFI), electronic spark advance (ESA), idle speed control (ISC) and exhaust gas recirculation (EGR). The electronic control unit (ECU) monitors engine intake air volume, intake air temperature, coolant temperature, engine rpm and exhaust oxygen content, and regulates engine operation. The TCCS has a self-diagnostic function that helps find malfunctions or abnormalities in the system.


ELECTRONIC FUEL INJECTION (EFI)

The ECU receives signals from various sensors indicating changing engine operations such as:

Intake Air Volume
Intake Air Temperature
Coolant Temperature
Engine RPM
Acceleration/Deceleration
Exhaust Oxygen Content etc..

The signals are used by the ECU to determine the proper injection duration necessary for an optimum air/fuel ratio.


EMISSION CONTROL SYSTEM

The ECU controls the Air Suction (AS) system according to coolant temperature, engine rpm, throttle valve angle, vehicle speed and intake air volume. These Emission Control Systems is activated by a vacuum switching valve (VSV).


ELECTRONIC SPARK ADVANCE (ESA)

The ECU is programmed with data for optimum ignition timing under any and all operating conditions. Using data provided by sensors which monitor various engine functions, (rpm, coolant temperature, etc..), the microcomputer triggers the spark at precisely the right instant.


SELF-DIAGNOSTIC FUNCTION

The ECU detects any malfunctions in the sensor network and lights a "CHECK ENGINE" warning light on the instrument panel. At the same time, the trouble is identified and a diagnosis code is recorded in the ECU memory. The diagnosis code can be read by the number of blinks of the "CHECK ENGINE" light when terminals TE1 and E1 are shorted together on the engine check connector.


FAIL-SAFE FUNCTION

In the event of major sensor malfunctioning, a back-up circuit will take over to provide minimal driveability, and the "CHECK ENGINE" light will illuminate.