Toyota CELICA 1990 All-Trac/4WD, Repair Manual

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* OXYGEN SENSOR HEATER CONTROL SYSTEM
THE 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 OXYGEN SENSOR TO IMPROVE DETECTION PERFORMANCE OF THE
SENSOR. THE ECU EVALUATES THE SIGNALS FROM EACH SENSOR (INPUT SIGNALS (1, 6, 8, 9, 11)), CURRENT IS OUTPUT TO
TERMINAL HT AND CONTROLS THE HEATER.
* ISC (IDLE SPEED CONTROL) SYSTEM
THE ISC SYSTEM (ROTARY SOLENOID TYPE) INCREASES THE RPM AND PROVIDES IDLING STABILITY FOR FAST IDLE–UP WHEN
THE ENGINE IS COLD AND WHEN THE IDLE SPEED HAS DROPPED DUE TO ELECTRICAL LOAD, ETC. THE ECU EVALUATES THE
SIGNALS FROM EACH SENSOR (INPUT SIGNALS (1, 4 TO 8, 11, 13)), OUTPUTS CURRENT TO TERMINALS RSC AND RSO AND
CONTROLS THE ISC VALVE.
* EGR CONTROL SYSTEM
WITH THE EGR CONTROL SYSTEM, THE ECU EVALUATES THE (INPUT SIGNALS (1, 4, 10)), FROM EACH SENSOR, CURRENT IS
OUTPUT TO TERMINAL EGR AND OPERATION OF THE EGR VALVE IS CONTROLLED.
* INTAKE AIR CONTROL SYSTEM
IN THE INTAKE AIR CONTROL SYSTEM, EACH CYLINDER IN THE INTAKE MANIFOLD IS DIVIDED INTO TWO PARTS, WITH AN INTAKE
AIR CONTROL VALVE INSTALLED IN THE PASSAGE ON ONE SIDE. THE OPENING AND CLOSING OF THE VALVE PROVIDES THE
MOST APPROPRIATE INTAKE AIR FLOW AND, AS WELL AS PREVENTING PERFORMANCE LOSS AT LOW SPEEDS, ALSO IMPROVES
FUEL ECONOMY. THE ECU EVALUATES THE SIGNALS FROM EACH SENSOR (INPUT SIGNALS (1, 4, 5)), OUTPUTS CURRENT TO
TERMINAL T–VIS CONTROLS THE VSV (FOR T–VIS) AND, CARRIES OUT OPENING AND CLOSING OF THE VALVE.
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 CHECK ENGINE WARNING LIGHT.
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 ECU MEMORY OR ELSE STOPS THE ENGINE.