General System Description

PURPOSE
The Toyota Computer Controlled System (TCCS) consists of sensors which detect various engine conditions and an Engine Control Module which controls the fuel injection timing, the self diagnostic function, the ignition timing control, the idle speed control, the fuel pressure control and the fuel pump control.

OPERATION
The TCCS controls these systems in the following manner;

Sequential Fuel Injection (SFI)
The engine control module receives signals from various sensors indicating changing engine operating conditions such as; Intake air volume, Engine speed, Intake air temperature, Acceleration/deceleration, Engine coolant temperature, Exhaust oxygen content etc.. These signals are utilized by the engine control module to determine the injection duration necessary for an optimum air-fuel ratio.

Electronic Spark Advance (ESA)
The engine control module is programmed with data for optimum ignition timing under all operating conditions. Again, using data provided by sensors which monitor various changing engine conditions the engine control module triggers the spark at precisely the right instant.

Idle Air Control (IAC)
The engine control module is programmed with target idling speed values to respond to different engine conditions (engine coolant temperature, air conditioning ON/OFF, etc.). Sensors transmit signals to the engine control module which control the flow of air through the throttle valve bypass and adjust idle speed to the target value.

Fail-Safe Function
In the event of a sensor malfunction, a backup circuit will take over to provide minimal driveability, and the malfunction indicator lamp will light up.

Diagnosis Function
When the engine control module detects a malfunction or abnormalities in the sensor network, it lights the malfunction indicator lamp in the combination meter. At the same time, the trouble is identified and a diagnostic trouble code is recorded by the engine control module. The diagnostic trouble codes and diagnostic system is explained in Testing and Inspection; Procedures.