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The engine control system utilizes a microcomputer and maintains overall control of the engine, transmission, etc. An outline of engine control is given here.

1. INPUT SIGNAL
1. Engine coolant temp. signal system
The engine coolant temp. sensor detects the engine coolant temp. and has a built-in thermistor with a resistance which varies according to the water temp. Thus the water temp. is input in the form of a control signal to TERMINAL THW of the engine control module.
2. Intake air temp. signal system
The intake air temp. sensor is installed inside the mass air flow meter and detects the intake air temp., which is input as a control signal to TERMINAL THA of the engine control module.
3. Heated oxygen sensor signal system
The oxygen density in the exhaust emissions is detected and input as a control signal to TERMINAL OXS of the engine control module. To maintain stable detection performance by the heated oxygen sensor, a heater is used for warming the sensor. The heater is also controlled by the engine control module (HTS).
4. RPM signal system
Camshaft position and crankshaft position are detected by the camshaft position sensor and crankshaft position sensor, camshaft position is input as a control signal to TERMINAL G2 of the engine control module, and engine RPM is input to TERMINAL NE+.
5. Throttle signal system
The throttle position sensor detects the throttle valve opening angle, which is input as a control signal to TERMINAL VTA of the engine control module.
6. Vehicle speed signal system
The vehicle speed sensor detects the vehicle speed and inputs a control signal to TERMINAL SP1 of the engine control module via the combination meter.
7. A/C SW signal system
The operating voltage of the A/C magnetic clutch is detected and input in the form of a control signal to TERMINAL AC1 of the engine control module.
8. Battery signal system
Voltage is constantly applied to TERMINAL BATT of the engine control module. When the ignition SW is turned to ON, voltage for engine control module operation is applied via the EFI relay to TERMINAL +B of the engine control module.
9. Intake air volume signal system
Intake air volume is detected by the mass air flow meter and a signal is input into TERMINAL VG of the engine control module as a control signal.
10. Stop light SW signal system
The stop light SW is used to detect whether or not the vehicle is braking and the information is input as a control signal to TERMINAL STP of the engine control module.
11. Starter signal system
To confirm that the engine is cranking, the voltage applied to the starter motor during cranking is detected and is input as a control signal to TERMINAL STA of the engine control module.
12. Engine knock signal system
Engine knocking is detected by the knock sensor 1 and 2 and the signals are input to TERMINALS KNK1 and KNK2 of the engine control module.
13. 4WD signal system
Whether or not the vehicle is operating in 4WD mode is determined, and a control signal is input to TERMINAL 4WD of the engine control module.
14. Air fuel ratio signal system
The air fuel ratio is detected and input as a control signal into TERMINAL AF1+ of the engine control module.

2. CONTROL SYSTEM
* SFI system
The SFI system monitors the engine conditions through the signals (Input signals (1 to 13)) input from each sensor to the engine control module. Based on this data and the program memorized in the engine control module, the most appropriate fuel injection timing is decided and current is output to TERMINALS #10, #20, #30, #40, #50 and #60 of the engine control module, causing the injectors to operate (to inject fuel). It is this system which, through the work of the engine control module, finely controls fuel injection in response to driving conditions.

* Electronic Spark Advance system
The ESA system monitors the engine conditions using the signals (input signals (1, 4, 5 to 7, 9, 11, 12)) input to the engine control module from each sensor. Based on this data and the program memorized in the engine control module, the most appropriate ignition timing is decided and current is output to TERMINALS IGT1, IGT2 and IGT3 of the engine control module. This output controls the igniter to produce the most appropriate ignition timing for the driving conditions.

* Heated oxygen sensor heater control system
The heated oxygen sensor heater control system turns the heater to on when the intake air volume is low (Temp. of exhaust emissions low), and warms up the heated oxygen sensor to improve detection performance of the sensor. The engine control module evaluates the signals (Input signals (1, 4, 8, 9, 11) ) from each sensor, current is output to TERMINAL HTS and controls the heater.

3. DIAGNOSIS SYSTEM
With the diagnosis system, when there is a malfunction in the ECU signal system, the malfunctioning system is recorded in the memory. The malfunctioning system can then be found by reading the display (Code) of the malfunction indicator lamp.

4. FAIL-SAFE SYSTEM
When a malfunction occurs in any system, if there is a possibility of engine trouble being caused by continued control based on the signals from that system, the fail-safe system either controls the system by using data (Standard values) recorded in the engine control module memory or else stops the engine.