Engine Controls - Theory & Operation Toyota Tercel L40

INTRODUCTION

This article covers basic description and operation of engine performance-related systems and components. Read this article before diagnosing vehicles or systems with which you are not completely familiar.

Camry 3.0L & Supra Non-Turbo

The Electronic Control Unit (ECU) controls amount of airflow into intake manifold by use of an air valve located in the air intake chamber. Operation of intake air control valve system provides increased power in low speed range.

The ECU uses an input RPM signal from distributor pick-up coil and throttle position sensor signal for determining intake air control valve system operation. The ECU controls ground circuit for intake air control valve system Vacuum Switch Valve (VSV), which provides vacuum to a vacuum tank. The vacuum tank supplies vacuum to an actuator valve which operates the air valve in the air intake chamber.

Celica Turbo & MR2 Turbo

Each intake manifold cylinder runner is divided into 2 parts. An intake air control valve is installed in one passage on each cylinder runner. Opening and closing of intake air control valve provides best possible airflow to prevent low-speed performance loss and improved fuel economy.

On Celica Turbo, ECU uses input RPM signal from distributor pick-up coil, throttle position signal and coolant temperature signal for determining intake air control valve operation.

On MR2 Turbo, ECU uses input RPM signal from distributor pick-up coil, throttle position signal, knock sensor signal and air intake volume signal for determining intake air control valve operation.

Note. The T-VIS VSV may also be referred to as the variable induction system VSV.

On all models, ECU controls ground circuit on a T-VIS Vacuum Switch Valve (VSV), which provides vacuum to a vacuum chamber for intake air control valve operation.

Celica Turbo, MR2 Turbo & Supra Turbo

All systems are equipped with an air-cooled intercooler and use a wastegate system to control maximum boost pressure. On Celica Turbo and MR2 Turbo, maximum boost pressure is controlled by the Electronic Control Unit (ECU) and a wastegate actuator.

A turbo pressure sensor delivers an input signal to the ECU, indicating the boost pressure. The ECU controls a turbocharging pressure Vacuum Switching Valve (VSV) which operates the wastegate actuator for boost pressure control.

On Supra Turbo, wastegate valve is operated by the actuator which receives a pressure signal from the intake manifold.

TOYOTA COMPUTER CONTROL SYSTEM (TCCS)

The TCCS is a computerized emission, ignition and fuel injection control system. The TCCS lowers exhaust emissions while maintaining good fuel economy and driveability. System consists of various sensors, switches and control units. (Scheme 1)-22.

An Electronic Control Unit (ECU) controls the TCCS based on input signals received from various input devices. The ECU contains preprogrammed data to maintain optimum engine performance under all operating conditions.

Scheme 1

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Scheme 22

CONTROL UNIT

The Electronic Control Unit (ECU) microprocessor receives input signals from various sensors, switches and ignition and starting system components. The ECU uses this information for controlling various functions. See OUTPUT SIGNALS .

The ECU has constant battery voltage at BATT terminal. The EFI main relay provides battery voltage to terminals +B and +B1 of ECU. The EFI main relay is activated when ignition is turned on.

The ECU contains a fail-safe function, used in case of sensor or switch failure. The fail-safe function uses preprogrammed values to provide a limp-in mode for minimal driveability or may shut off engine.

The ECU is equipped with a self-diagnostic function. Trouble codes are set by the malfunction of various engine sensors, switches or circuits and stored in the ECU memory. When trouble code is stored, the CHECK ENGINE light on the instrument panel will come on.

ECU LOCATION

Note. Components are grouped into 2 categories. The first category is INPUT DEVICES, which covers components that control or produce voltage signals monitored by the control unit. The second category is OUTPUT SIGNALS, which are components controlled by the control unit.

INPUT DEVICES

Vehicles are equipped with different combinations of input devices. Not all devices are used on all models. To determine the input device usage on a specific model, see appropriate wiring diagram in WIRING DIAGRAMS article in the ENGINE PERFORMANCE Section. The available input signals include the following

A/C Switch

When A/C is turned on, an input signal is delivered to the ECU. The ECU uses input signal for controlling engine idle speed during A/C operation.

Airflow Sensor (Except Camry 2.2L, Celica 1.6L 4A-FE & 2.2L 5S-FE, Corolla, MR2 2.2L, Paseo & Tercel)

On all models except Supra Turbo, the airflow sensor, located in the airflow meter, measures airflow volume. Airflow meter converts intake air readings into a voltage signal by means of a variable resistor (potentiometer).

On Supra Turbo, airflow volume is measured by a Karman-Vortex airflow meter, which uses a mirror and photo transistor to measure air-flow volume. On all models, input signal is sent to ECU for controlling fuel injection duration and ignition timing (spark advance).

Battery Signal

Battery voltage is always present at BATT terminal of ECU. When ignition is turned on, voltage for ECU operation is applied through EFI main relay to terminals +B and +B1.

Brakelight Signal

Brakelight switch delivers an input signal to STP terminal of ECU to indicate when brakes are applied.

Coolant Temperature Sensor (CTS)

The CTS contains a built-in thermistor in which resistance varies according to engine coolant temperature. The CTS delivers an input signal to THW terminal of the ECU. The ECU uses input signal for controlling air injection system (if equipped), fuel injection duration, overdrive operation on electronically controlled transmissions, ignition timing (spark advance), idle speed control system and EGR system.

Coolant Temperature Switch (Land Cruiser & Paseo A/T)

Coolant temperature switch contacts close when coolant temperature exceeds a specified temperature and delivers an input signal to ECU at the TWS terminal. The ECU uses input signal for operating Vacuum Switching Valve (VSV) for the fuel pressure control system.

Electrical Load Signal (Camry 2.2L, Celica Turbo & 2.2L 5S-FE, Corolla, MR2 & Paseo)

An input signal is delivered to the ECU to indicate when high electrical output is required. This signal will be delivered when items such as, rear window defroster, headlights, etc. are turned on. The ECU uses input signal to maintain proper idle speed.

Engine Cranking Signal

While engine is cranking, voltage applied to the starter is also delivered to STA terminal of ECU.

EGR Gas Temperature Sensor

EGR gas temperature sensor monitors EGR gas temperature and delivers an input signal to ECU.

Intake Air Temperature Sensor

An air temperature sensor is mounted in either airflow meter or air filter housing. Air temperature sensor measures intake air temperature and delivers a input signal to the ECU for controlling fuel injection duration.

Knock Sensor

Knock sensor monitors ignition knock conditions and delivers an input signal to the ECU. The ECU uses input signal to determine ignition timing (spark advance).

Neutral/Start Switch (A/T)

The neutral/start switch delivers an input signal, indicating gear position, to NSW terminal of ECU. ECU uses information to allow starter operation and control engine idle.

Oil Pressure Switch Signal (Supra Turbo)

Oil pressure switch delivers an input signal at OIL terminal of ECU. The ECU uses this input signal to monitor the oil pressure.

Oxygen (O2) Sensor

Oxygen sensor monitors exhaust gas oxygen content and delivers an input signal to the ECU. The ECU uses input signal to determine fuel injection duration. Some models are equipped with more than one oxygen sensor and a sub-oxygen sensor. Some models may contain a heater used to warm the oxygen sensor.

RPM Signal

On all models except Supra Turbo, crankshaft position and engine RPM are detected by pick-up coils in the distributor. The ECU uses this information for controlling engine operation.

On all models except Tercel, Pickup 2.4L and 4Runner 2.4L, crankshaft position input signal is delivered to terminal G, G+ or G1 (and G2 on some models) of ECU and engine RPM input signal is delivered to terminal NE or NE+ of ECU.

Tercel, Pickup 2.4L and 4Runner 2.4L use a single pick-up coil and input signal is delivered to terminal NE of ECU.

On Supra Turbo, crankshaft position and engine RPM are detected by camshaft position sensor. Crankshaft position input signal is delivered to terminals G1 and G2 of ECU and engine RPM input signal is delivered to terminal NE of ECU.

Sub-Oxygen Sensor (California Only)

Sub-oxygen sensor is used in conjunction with the oxygen sensor. Sub-oxygen sensor monitors exhaust gas oxygen content and delivers an input signal to the ECU. The ECU uses input signal to determine fuel injection duration.

Throttle Position Sensor (TPS)

The TPS, mounted on throttle body, delivers an input signal indicating throttle valve position to the ECU. The ECU uses input signal for controlling fuel injection system and automatic transmissions/transaxles (some models).

Turbocharging Pressure Sensor (Celica Turbo & MR2 Turbo)

Turbocharging pressure sensor delivers an input signal to the ECU, indicating the boost pressure. The ECU uses this signal to control the turbo boost pressure.

Vacuum Sensor (Camry 2.2L, Celica 1.6L 4A-FE & 2.2L 5S-FE, Corolla, MR2 Non-Turbo, Paseo & Tercel)

Vacuum sensor may also be referred to as Manifold Absolute Pressure (MAP) sensor. Vacuum sensor monitors intake manifold intake air volume and delivers an input signal to the ECU. The ECU uses input signal for controlling fuel injection duration.

Vehicle Speed Sensor

Vehicle speed sensor, located in the instrument cluster, monitors vehicle speed and delivers an input signal to the ECU. The ECU uses input signal for controlling fuel injection, air injection (if equipped), cruise control and electronic control of automatic transmission/transaxle (some models).

4WD Switch (Land Cruiser, Pickup & 4Runner)

The 4WD switch delivers an input signal to the ECU to indicate 4WD operation.

OUTPUT SIGNALS

Note. Vehicles are equipped with different combinations of computer-controlled components. Not all components listed below are used on every vehicle. For theory and operation on each output component, refer to system indicated after component.

The ECU receives input from data sensors and, depending on model application, controls the following components and sub-systems

A/C Cut Control System

See IDLE SPEED under FUEL SYSTEM.

A/C Idle-Up System

See IDLE SPEED under FUEL SYSTEM.

Air Injection System Vacuum Switching Valve (VSV)

See EMISSION SYSTEMS.

Air Suction System Vacuum Switching Valve (VSV)

See EMISSION SYSTEMS.

Circuit Opening Relay

See FUEL DELIVERY under FUEL SYSTEM.

Electronic Spark Advance

See ELECTRONIC IGNITION SYSTEM under IGNITION SYSTEM.

EGR System Vacuum Switching Valve (VSV)

See EXHAUST GAS RECIRCULATION (EGR) SYSTEM under EMISSION SYSTEMS.

Electronically Controlled Transmission/Transaxle (ECT)

See MISCELLANEOUS CONTROLS.

Fuel Pressure Control System Vacuum Switching Valve (VSV)

See FUEL DELIVERY under FUEL SYSTEM.

Fuel Pump

See FUEL DELIVERY under FUEL SYSTEM.

Idle Speed Control System

See IDLE SPEED under FUEL SYSTEM.

Idle-Up System

See IDLE SPEED under FUEL SYSTEM.

Intake Air Control Valve System

See AIR INDUCTION SYSTEM.

Oxygen Sensor Heater

See FUEL CONTROL under FUEL SYSTEM.

Self-Diagnostic System

See SELF-DIAGNOSTIC SYSTEM.

Turbocharging Vacuum Switching Valve (VSV)

See AIR INDUCTION SYSTEM.

Variable Induction System Vacuum Switching Valve (VSV)

See AIR INDUCTION SYSTEM.

EFI Main Relay

The EFI fuse supplies constant battery voltage to EFI main relay. EFI main relay provides battery voltage to +B terminal of circuit opening relay and engine check connector. Depending on model, EFI main relay may either be turned on directly by ignition switch or by M-REL terminal of Electronic Control Unit (ECU).

Circuit opening relay controls fuel pump circuit. The Electronic Control Unit (ECU) receives an input signal at STA terminal when engine is cranking. Starter signal is also applied to terminal STA of circuit opening relay.

Starter signal energizes circuit opening relay during cranking. Circuit opening relay then provides voltage to fuel pump or fuel pump relay. Celica Turbo, Cressida, MR2 Turbo and Supra use fuel pump relay.

On all models except Camry 2.2L, Celica, Corolla, MR2, Paseo, Supra Turbo and Tercel, fuel pump switch in airflow meter provides ground for circuit opening relay. On all other models, circuit opening relay is grounded by the ECU through the FC terminal.

Fuel Pump Relay & Fuel Pump Resistor (Celica Turbo, Cressida, MR2 Turbo & Supra)

Fuel pump relay receives voltage from circuit opening relay and operates the fuel pump. Fuel pump operating speed may be varied by the ECU based on intake air volume and engine RPM signal. When ECU grounds fuel pump relay, relay contacts close and voltage is supplied through fuel pump resistor to the fuel pump. This changes the fuel pump operating speed.

Fuel pump is mounted in the fuel tank and contains an internal check valve. Fuel pump can be operated with ignition off by installing jumper wire between +B and FP terminals of engine check connector. On Celica Turbo, Cressida, MR2 Turbo and Supra, fuel pump operating speed may be varied by the use of fuel pump relay and fuel pump resistor.

Fuel Pressure Regulator

Mounted on the fuel rail, vacuum operated fuel pressure regulator maintains constant fuel pressure to the fuel injectors. As throttle is depressed and manifold vacuum decreases, fuel pressure regulator increases fuel pressure to maintain a constant fuel flow to the fuel injectors.

Note. Fuel pressure control system may also be referred to as fuel pressure-up system.

Fuel Pressure Ctrl Sys (Camry 3.0L, Land Cruiser, MR2 Non-Turbo, Paseo, Pickup, Previa, Supra Turbo, Tercel & 4Runner)

Fuel pressure control system increases fuel pressure slightly on hot restarts for improved starting and idle stability. Fuel pressure increase is obtained by shutting off vacuum supply to fuel pressure regulator. The ECU controls vacuum supply to fuel pressure regulator by operating fuel pressure control system Vacuum Switching Valve (VSV). Increased fuel pressure will exist for about 90 seconds after the hot restart.

Fuel Pulsation Damper

Some models use a fuel pulsation damper mounted on fuel deliver pipe to eliminate fuel line pressure surges caused by fuel injector operation.

Cold Start Injector

Cold start injector delivers additional fuel during cold engine starts. Cold start injector receives voltage from ignition switch during engine cranking. Ground circuit for cold start injector is controlled by cold start injector time switch.

Cold Start Injector Time Switch

Cold start injector time switch determines cold start injector on time for cold engine starting. Cold start injector ground circuit is controlled by cold start injector time switch, located in an engine coolant passage.

Fuel-Cut System

Controlled through input from the throttle position sensor, the ECU will cut (shut off) fuel delivery during closed throttle deceleration.

Fuel Injectors

Fuel injectors are ECU actuated solenoids which deliver fuel to individual cylinders. The ECU controls fuel injector duration based on various input signals to determine the air/fuel mixture.

Note. Injector resistor may also be referred to as solenoid resistor.

Injector Resistor (Celica Turbo, MR2 Turbo & Supra Turbo)

Injector resistor reduces current flow to the fuel injectors.

On some models, oxygen sensor may be equipped with a heating element. The ECU activates the oxygen sensor heater when intake air volume and coolant temperature are low, warming the oxygen sensor for improved performance.

A/C Cut Control System (Camry 2.2L, Celica 1.6L 4A-FE & 2.2L5S-FE, Corolla, MR2 Non-Turbo, Paseo & Previa)

The A/C cut control system interrupts A/C compressor operation for a fixed period of time when vehicle accelerates from low engine speed. On Corolla, A/C operation is also interrupted when engine speed is less than 500 RPM to prevent engine stalling.

On all models except Celica 1.6L 4A-FE, Corolla, Paseo and Previa, ECU uses vehicle speed and throttle valve angle input signals to determine A/C cut control system operation. On Previa, ECU uses throttle valve angle input signal to determine A/C cut control system operation. On all other models, ECU uses vehicle speed, throttle valve angle, vacuum sensor and neutral/start switch input signals to determine A/C cut control system operation.

A/C Idle-Up System (Camry 2.2L & Celica 2.2L 5S-FE)

A/C idle-up system provides a stable idle speed when A/C is operating. ECU controls A/C idle-up Vacuum Switching Valve (VSV). A/C idle-up VSV allows extra intake air to by-pass throttle valve for increased idle speed.

Note. Auxiliary air valve may also be referred to as the air valve.

Auxiliary Air Valve (Celica 1.6L 4A-FE, Paseo, Pickup, Tercel & 4Runner)

Auxiliary air valve provides additional air to intake manifold when engine is cold for increased idle speed. Auxiliary air valve is mounted on throttle body and determines engine temperature by engine coolant being routed around the valve.

Idle Speed Control System (Camry, Celica Turbo & 2.2L 5S-FE, Corolla, Cressida, Land Cruiser, MR2, Previa & Supra)

The ECU is programmed with engine idle speed values. The Idle Speed Control (ISC) system provides a stable idle speed when engine is cold and idle speed decreases due to electrical load.

An input signal is delivered to the ECU, indicates when high electrical output is required. Input signal is delivered when items such as, rear window defroster, headlights, etc. are turned on. The ECU uses input signal along with other various input signals to maintain proper idle speed by controlling ISC valve located on air intake system.

Idle-Up System (Celica 1.6L 4A-FE, Corolla & Tercel)

Idle-up system provides a stable idle speed when idle speed decreases due to electrical load. An input signal is delivered to the ECU, indicating when high electrical output is required. Input signal will be delivered when items such as rear window defroster, headlights, etc. are turned on.

The ECU uses input signal along with other input signals to maintain proper idle speed by controlling the idle-up Vacuum Switching Valve (VSV). The idle-up VSV allows extra intake air to by-pass the throttle valve for increased idle speed.

Supra Turbo

The distributorless ignition system uses the Electronic Control Unit (ECU) for determining ignition timing (spark advance). The ECU determines ignition timing (spark advance) based on various input signals. Various input signals which may be used are coolant temperature sensor, airflow meter, engine RPM, throttle position sensor, vehicle speed sensor, neutral switch, A/C switch, cranking (starter) signal and knock sensor.

Conventional distributor and pick-up coil have been replaced by a camshaft position sensor. Crankshaft position input signal is delivered to terminal G1 and G2 of ECU and engine RPM input signal is delivered to terminal NE of ECU. (Scheme 23)

The ECU uses 3 ignition primary control signals for the ignition coils as IGT, IGDA and IGDB terminals of ECU. The ECU monitors the IGF circuit to ensure ignition coil has fired.

Scheme 23

ELECTRONIC IGNITION SYSTEM

Note. The electronic ignition system may be referred to as the Electronic Spark Advance (ESA).

Except Supra Turbo

The electronic ignition system uses the Electronic Control Unit (ECU) for determining ignition timing (spark advance). The ECU determines ignition timing (spark advance) based on various input signals. Various input signals that may be used are: coolant temperature sensor, oxygen sensor, engine RPM, vehicle speed sensor, A/C switch, 4WD operation (Pickup and 4Runner), airflow meter, knock sensor, vacuum sensor and cranking (starter) signal. Input signals may vary on model application. Integrated (ignition coil in distributor) and remote ignition coil designs are used depending on model.

On Tercel, Pickup 2.4L and 4Runner 2.4L, a single pick-up coil in the distributor delivers crankshaft position and engine RPM input signal to the ECU. The ECU monitors pick-up coil signal at NE terminal. On all other models, crankshaft position and engine RPM input signals are delivered to the ECU by 2 pick-up coils in the distributor. Crankshaft position input signal is delivered to terminal G, G+ or G1 (and G2 on some models) of ECU and engine RPM input signal is delivered to terminal NE or NE+ of ECU. (Scheme 24)

On all models, ECU uses pick-up coil input signals to switch primary ignition circuit on and off. Primary circuit is turned off when ECU delivers a signal to the ignitor on the IGT wire, causing ignition coil to fire the spark plug. After delivering a command to turn off primary circuit on the IGT wire, the ECU monitors the IGF circuit to ensure primary switching occurred. (Scheme 24)

Scheme 24

Land Cruiser

Air Injection System (AIS) is used to reduce hydrocarbon (HC) and carbon monoxide (CO) emissions by injecting air into the exhaust manifold. Fresh air is drawn from air cleaner and compressed by the air pump and delivered to the Air Suction Valve (ASV). (Scheme 25) Using the ASV and air injection system Vacuum Switching Valve (VSV), compressed air is injected into exhaust manifold or exhausted into the atmosphere as determined by ECU.

The ECU controls air injection system VSV based on various input signals such as coolant temperature and engine operating conditions. For specific system operating parameters and testing of system or components, see AIR INJECTION SYSTEM (LAND CRUISER) under EMISSION SYSTEMS & SUB-SYSTEMS in I - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section.

Scheme 25

AIR SUCTION SYSTEM

Note. Air suction system may be referred to as pulse air system.

Pickup & 4Runner

The Air Suction (AS) system uses exhaust gas pulses to draw air into exhaust port to reduce hydrocarbon (HC) and carbon monoxide (CO) emissions when engine is cold and during deceleration. The AS system draws air through resonator and air suction reed valve and into exhaust port. (Scheme 26)

The ECU controls air suction system Vacuum Switching Valve (VSV) based on various input signals. Various input signals such as coolant temperature, engine RPM, throttle valve position, vehicle speed sensor, intake airflow, A/C switch signal and cranking signal may be used, depending on vehicle application.

For specific system operating parameters and system and component testing, see AIR SUCTION (AS) SYSTEM (PICKUP & 4RUNNER) under EMISSION SYSTEMS & SUB-SYSTEMS in I - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section.

Scheme 26

CRANKCASE VENTILATION

The Positive Crankcase Ventilation (PCV) system prevents crankcase hydrocarbon (HC) vapors from escaping into the atmosphere. Crankcase vapors are routed from crankcase through a vacuum controlled fixed orifice or PCV valve, into the intake manifold. In the intake manifold, crankcase vapors are mixed with air/fuel mixture and delivered into the cylinders. (Scheme 27)and (Scheme 28).

PCV system provides primary control of crankcase blow-by vapors, according to manifold vacuum. When manifold vacuum is high (at idle), PCV restricts vapor flow to maintain a smooth idle condition.

Scheme 27

Scheme 28

EXHAUST GAS RECIRCULATION (EGR) SYSTEM

The EGR system reduces oxides of nitrogen (NOx) emissions by lowering combustion temperatures. Combustion temperatures are lowered by recycling metered amounts of exhaust gases back into the intake system.

The EGR system contains a vacuum-operated EGR valve and a vacuum modulator. (Scheme 29) A check valve, EGR cooler and EGR Vacuum Switching Valve (VSV) may also be used. Vacuum modulator regulates exhaust backpressure and balances atmospheric pressure and vacuum to allow EGR operation at heavy throttle. The EGR cooler, used on Cressida and Supra models, assists in reducing exhaust gas temperature before entering combustion chamber.

Camry 3.0L, Previa, Pickup 2.4L Federal and 4Runner 2.4L use a Bimetallic Vacuum Switching Valve (BVSV) to control EGR operation. The BVSV, mounted in engine coolant passage, opens at specified temperature, allowing EGR operation.

On all other models, the Electronic Control Unit (ECU) controls the EGR VSV for EGR operation. The ECU uses input signals such as coolant temperature, engine RPM, throttle position, brakelight switch and intake air volume for controlling the EGR VSV. Input signals may vary by vehicle application. Various model and engine types will have different EGR system components and operating parameters. For specific EGR operating parameters and testing of system or components on various models, see EXHAUST GAS RECIRCULATION (EGR) under EMISSION SYSTEMS & SUB-SYSTEMS in I - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section.

Scheme 29

EVAPORATIVE EMISSION (EVAP) SYSTEM

Note. The EVAP may also be referred to as fuel evaporation.

The EVAP system prevents fuel tank gasoline vapors from escaping into the atmosphere. Fuel tank gasoline vapors are routed through charcoal canister into intake manifold for combustion in the cylinders. (Scheme 30) Some models use a Bimetallic Vacuum Switching (BVSV) mounted in the engine coolant passage. The BVSV controls the EVAP system in relation to engine coolant temperature.

Various model and engine types will have different evaporative emission system components and operating parameters. For specific EVAP system operating parameters and system and component testing, see FUEL EVAPORATION under EMISSION SYSTEMS & SUB-SYSTEMS in I - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section.

Scheme 30

Electronic Control Unit (ECU) is equipped with self-diagnostic system. By analyzing various input signals, ECU detects system malfunctions related to various operating parameters. When malfunction occurs, CHECK ENGINE light on instrument panel is activated and fault code is stored in ECU memory. For additional information on self-diagnostic system, see appropriate TESTS W/CODES article in the ENGINE PERFORMANCE Section.

TRANSMISSION CONTROLS

Note. Only electronically controlled transmissions/transaxles are covered. Some models have transmissions and transaxles that are not electronically controlled.

Supra uses a separate control unit for the ECT. The engine ECU transmits a signal to ECT control unit for overdrive operation. The engine ECU uses input from coolant temperature sensor to prevent a shift into overdrive when engine is cold. On models that do not have a separate control unit for ECT, engine ECU controls all shift functions.

See also:
• OUTPUT SIGNALS