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.


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.


IDLE SPEED CONTROL (ISC)

The ECU is programmed with target idling speed values to respond to different engine conditions, (coolant temperature, air conditioner on/off, etc.). Sensors transmit signals to the ECU which control the flow of air through the idle bypass of the throttle valve and adjust idle speed to the target value.


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.