The engine is equipped with a Toyota Computer Control System (TCSS) which centrally controls the electronic fuel injection, electronic spark advance and the exhaust gas recirculation valve. The systems can be diagnosed by means of an Electronic Control Unit (ECU) which employs a microcomputer. The ECU and the TCCS control the following functions:
Electronic Fuel Injection (EFI). The ECU receives signals from the various sensors indicating changing engine operations conditions such as:
Intake air volume
These signals are utilized by the ECU to determine the injection duration necessary for an optimum air/fuel ratio.
- The Electronic Spark Advance (ESA) is programmed with data for optimum ignition timing during any and all operating conditions. Using the data provided by sensors which monitor various engine functions (rpm, intake air volume, coolant temperature, etc.), the microcomputer (ECU) triggers the spark at precisely the right moment.
- Idle Speed Control (ISC) is programmed with specific engine speed values to respond to different engine conditions (coolant temperature, air conditioner on/off, etc.). Sensors transmit signals to the ECU which controls the flow of air through the by-pass of the throttle valve and adjusts the idle speed to the specified value.
- Exhaust Gas Recirculation (EGR) detects the coolant temperature and controls the EGR operations accordingly.
- Electronic Controlled Transmission (ECT-automatic transmission only). A serial signal is transmitted to the ECT computer to prevent shift up to third or overdrive during cold engine operation.
- Diagnostics, which are outlined below.
- Fail-safe function. In the event of a computer malfunction, a backup circuit will take over to provide minimal driveability. Simultaneously, the "CHECK ENGINE" warning light is activated.