GS300
ACIS is a variable induction system that improves engine performance by increasing the length of the intake runners in the air intake chamber. ECM controls the ACIS Vacuum Switching Valve (VSV). VSV is an electric solenoid that controls vacuum supply to the ACIS actuator. ACIS actuator opens and closes an Intake Air Control Valve (IACV), which increases the length of the intake runners. ACIS vacuum tank is a vacuum reservoir.
COMPUTERIZED ENGINE CONTROLS
Note. For component locations, see COMPONENT LOCATIONS under INTRODUCTION in SYSTEM/COMPONENT TESTS article.
ELECTRONIC CONTROL MODULE (ECM)
ECM controls engine operation based on input signals from various sensors. ECM also controls transmission. If self-diagnostic system detects a fault, it stores a trouble code in the ECM memory, and turns on the Malfunction Indicator Light (MIL), also known as CHECK ENGINE light. For more information, see TESTS W/CODES article.
If the ECM detects a system fault, it controls fuel injection and ignition timing at predetermined levels as a back-up (fail-safe) function to make it possible to continue vehicle operation. If engine speed exceeds 6500 RPM, ECM stops fuel injection until engine speed decreases to less than 6500 RPM. This prevents engine overrun.
Back-Up (Constant) Power
Battery power is supplied at all times to the ECM through the EFI fuse.
Ignition Keyed Power
When the ignition switch is turned on, the ECM grounds the control circuit (coils) of the EFI main relay. This supplies battery power to the ECM. This circuit is also protected by the EFI fuse.
Note. Components are grouped into 2 categories. The first category covers INPUT DEVICES, which control or produce voltage signals monitored by the control unit. The second category covers OUTPUT SIGNALS, which are components controlled by the control unit.
A/C Request
ECM senses when A/C is turned on, and uses this signal to increase idle speed.
Cruise Control ECU
ECM applies a reference voltage to cruise control ECU. When cruise control is engaged, cruise control ECU grounds the reference voltage.
Distributor Pick-Up Coils
Distributor contains 3 permanent magnet pick-up coils and a reluctor, which is mounted on the distributor shaft. When the reluctor passes by a pick-up coil, AC voltage is induced in the pick-up coil. The ECM uses the signals from pick-up coils G1 and G2 to determine TDC of cylinder No. 1. The ECM uses the signal from pick-up coil NE to determine incremental crankshaft position and engine speed. ECM uses these signals to control fuel injection duration and ignition timing. For more information, see IGNITION SYSTEM.
EGR Temperature Sensor
ECM applies a reference voltage to EGR temperature sensor, which is a variable resistor. Value of reference voltage corresponds to volume of exhaust gas that is entering the intake system.
Engine Coolant Temperature (ECT) Sensor
ECM applies a reference voltage to ECT sensor, which is a variable resistor. ECM uses voltage signal to control fuel injection duration.
Ignitor
Each time the ignition coil(s) fire, the ECM receives a signal from the ignitor. If the ECM does not receive this signal, it shuts off fuel injection.
Intake Air Temperature (IAT) Sensor
IAT sensor is part of volume airflow sensor. ECM applies a reference voltage to IAT sensor, which is a variable resistor. ECM uses voltage signal to control fuel injection duration.
Knock Sensors
A piezoelectric ceramic element is incorporated within each knock sensor. If engine knocking occurs because of detonation, the piezoelectric element vibrates, generating voltage. Based on this voltage signal, ECM retards ignition timing.
Oxygen Sensor
Oxygen sensor generates voltage that the ECM uses to determine fuel injection duration. Some oxygen sensors are heated by an electric heater element.
Park/Neutral Position (PNP) Switch
PNP switch controls voltage signals to ECM to indicate transmission gear position.
Starter Signal
During engine cranking, voltage is applied to ECM.
Sub-Throttle Position (Sub-TP) Sensor (With TRAC)
Vehicles with Traction Control (TRAC) system are equipped with a secondary (sub) throttle plate that is controlled by an electric actuator. The ECM monitors the angle of this sub-throttle plate by applying a reference voltage to the sub-TP sensor, which operates like the TP (main) sensor. Sub-TP sensor also contains an idle switch.
Throttle Position (TP) Sensor
ECM monitors the angle of the throttle plate by applying a reference voltage to the TP sensor, which contains a potentiometer and an idle switch.
Vehicle Speed Sensor (VSS)
VSS detects rotation speed of transmission/transaxle output shaft and sends signals to ECM. The ECM determines vehicle speed based on these signals.
Volume Airflow (VAF) Sensor
ECM determines airflow volume by applying a reference voltage to VAF sensor, which contains a Karman-Vortex unit. ECM uses signal to control fuel injection duration and spark advance.
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 of each output component, refer to system indicated after component.
A/C Clutch
See A/C SYSTEM under MISCELLANEOUS CONTROLS.
A/C Idle-Up System
See A/C SYSTEM under MISCELLANEOUS CONTROLS.
ACIS VSV
See ACOUSTIC CONTROL INDUCTION SYSTEM (ACIS).
EFI Main Relay
See ECM POWER SOURCE under COMPUTERIZED ENGINE CONTROLS.
EGR Valve
See EMISSION SYSTEMS.
EGR VSV
See EMISSION SYSTEMS.
Electronically Controlled Transmission/Transaxle
See TRANSMISSION/TRANSAXLE under MISCELLANEOUS CONTROLS.
EVAP Canister VSV
See EMISSION SYSTEMS.
Fuel Injectors
See FUEL CONTROL under FUEL SYSTEM.
Fuel Pressure Regulator VSV
See FUEL DELIVERY under FUEL SYSTEM.
Fuel Pump
See FUEL DELIVERY under FUEL SYSTEM.
Fuel Pump ECU
See FUEL DELIVERY under FUEL SYSTEM.
Idle Air Control (IAC) Valve
See IDLE SPEED under FUEL SYSTEM.
See IGNITION SYSTEM.
Malfunction Indicator Light
See SELF-DIAGNOSTIC SYSTEM.
Oxygen Sensor Heater Control
See EMISSION SYSTEMS.
Self-Diagnostics
See SELF-DIAGNOSTIC SYSTEM.
FUEL SYSTEM
Note. For component locations, see COMPONENT LOCATIONS under INTRODUCTION in SYSTEM/COMPONENT TESTS article.
Fuel Pressure Pulsation Damper
Damper lessens the effects of fuel pressure surges that occur when the injectors open.
Fuel Pressure Regulator
Fuel pressure regulator controls fuel pressure by regulating the amount of fuel that is returned to the fuel tank through the fuel return pipe.
Fuel Pressure Regulator Vacuum Switching Valve (VSV) (Except GS300 With Federal Emissions)
During starting in hot ambient temperatures, the ECM energizes the fuel pressure regulator VSV. When the VSV is energized, vacuum is prevented from being applied to the fuel pressure regulator diaphragm, which increases fuel pressure. This prevent vapor lock in the fuel system, and richens the air/fuel mixture to improve starting ability and idle quality.
In-tank, turbine fuel pump assembly consists of a motor and pump. A check valve and relief valve are also incorporated into pump assembly.
Fuel Pump Control
Fuel pump comes on when fuel pump ECU supplies voltage to fuel pump. The ECM controls the fuel pump ECU.
Fuel pump ECU can supply 9 volts (low speed) or 12 volts (high speed) to the fuel pump. The ECM controls the fuel pump ECU. During engine starting and high engine loading, the ECM commands the fuel pump ECU to output 12 volts to the fuel pump. Under all other conditions, the ECM commands the fuel pump ECU to output 9 volts to the fuel pump.
Fuel injector is energized when the ECM grounds the injector's circuit.
Fuel Pressure Control (Except GS300 With Federal Emissions)
During starting in hot ambient temperatures, the ECM energizes the fuel pressure regulator VSV. When the VSV is energized, vacuum is prevented from being applied to the fuel pressure regulator diaphragm, which increases fuel pressure. This prevents vapor lock in the fuel system, and richens the air/fuel mixture to improve starting ability and idle quality. This boosted condition should not last for more than 2 minutes.
Fuel Pump Speed Control
Under normal driving conditions (low engine speed or low engine load), the fuel pump ECU applies 9 volts to the fuel pump. When the engine requires more fuel, the fuel pump ECU applies 12 volts to the fuel pump.
See A/C SYSTEM under MISCELLANEOUS CONTROLS.
IAC valve is a stepper motor that is controlled by the ECM. The stepper motor contains a valve that controls the volume of intake air that by-passes the throttle valve.
IGNITION SYSTEM
Note. For component locations, see COMPONENT LOCATIONS under INTRODUCTION in SYSTEM/COMPONENT TESTS article.
IGNITION TIMING & SPARK ADVANCE
The ECM controls ignition timing and spark advance based on inputs from sensors.
TRIGGERING SIGNALS
Distributor contains 3 permanent magnet pick-up coils and a reluctor. When the reluctor on the distributor shaft passes by a pick-up coil, AC voltage is induced in the pick-up coil. The ECM uses the signals from pick-up coils G1 and G2 to determine TDC of cylinder No. 1. The ECM uses the signal from pick-up coil NE to determine incremental crankshaft position and engine speed.
IGNITOR(S)
Ignitor keeps the ignition coil primary circuit grounded, allowing a magnetic field to be built up in the ignition coil. When the ECM signals the ignitor, the ignitor interrupts the primary circuit, causing the ignition coil to fire.
EMISSION SYSTEMS
Note. For component locations, see COMPONENT LOCATIONS under INTRODUCTION in SYSTEM/COMPONENT TESTS article.
DASHPOT
Dashpot momentarily holds the throttle plate slightly open on deceleration.
EGR SYSTEM
When vacuum is applied to diaphragm in EGR valve, EGR valve pintle opens, allowing exhaust gas to enter intake system. The level of vacuum that is applied to the EGR valve determines the volume of exhaust gas that enters the intake system.
To control this level of vacuum, a diaphragm in the EGR vacuum modulator responds to exhaust gas backpressure. As the diaphragm moves, it moves a valve that controls the level of vacuum that is applied to the EGR valve.
If the ECM detects one or more of the following conditions, it turns on the Vacuum Switching Valve (VSV), which shuts off the vacuum supply to the EGR valve
- Engine coolant temperature is low
- Full deceleration has just occurred (throttle valve closed)
- Engine load is light (intake air volume is low)
- Engine speed is high.
EVAP (EVAPORATIVE) EMISSION SYSTEM
ECM controls canister purge by turning on a Vacuum Switching Valve (VSV). A check valve is installed in the vacuum line between the intake manifold and the VSV. A check valve attached to hose at bottom of EVAP canister allows air to enter canister, but prevents vapors from escaping.
Canister purge is controlled by a bimetallic thermal valve that responds to coolant temperature. As coolant temperature increases to 138°F (59°C), the thermal valve opens, allowing vacuum to be applied to the EVAP canister. As coolant temperature decreases to 104°F (40°C), the thermal valve closes. The valve will not open again until coolant temperature reaches 138°F (59°C). A check valve on hose at bottom of EVAP canister allows air to enter canister and prevents vapor loss.
FUEL-CUT SYSTEM (DECELERATION)
During deceleration from high engine speed with throttle valve completely closed, the ECM stops fuel injection to improve fuel economy and lower exhaust emissions.
When engine speed falls below a predetermined RPM or throttle valve is opened, fuel injection is resumed. Fuel cut-off and fuel injection resumption speeds are high when coolant temperature is low.
The ECM controls the operation of the oxygen sensor heater according to intake air volume and engine speed. If engine load is light and exhaust gas temperature is low, the heater is turned on to maintain sensor efficiency. When engine load is high and exhaust temperature is high, the heater is turned off to prevent deterioration of the sensor.
POSITIVE CRANKCASE VENTILATION (PCV)
PCV system routes fuel vapors from the crankcase into the intake manifold. PCV valve meters the flow of vapors according to manifold vacuum. When manifold vacuum is high (at idle), PCV valve restricts flow to maintain smooth idle.
THROTTLE OPENER
Throttle opener momentarily holds the throttle plate slightly open on deceleration.
MISCELLANEOUS CONTROLS
Note. Although not considered true engine performance-related systems, some controlled devices may affect driveability if they malfunction.
Note. For component locations, see COMPONENT LOCATIONS under INTRODUCTION in SYSTEM/COMPONENT TESTS article.
The ECM indirectly controls the operation of the A/C clutch. If the ECM detects that the A/C switch has been turned on(A/C request), ECM signals the A/C control assembly. The A/C control assembly then grounds the coil circuit of the A/C clutch relay. The relay contacts close, allowing power to the A/C clutch.
A/C Cut Control System
The ECM indirectly controls the operation of the A/C clutch. Under certain operating conditions (engine temperature too high, etc.), the ECM will not allow A/C clutch engagement.
When A/C compressor clutch engages, the ECM increases engine idle speed using the Idle Air Control (IAC) valve.
TRANSMISSION/TRANSAXLE
Note. For more information, see the TRANSMISSION SERVICING article.
This system electronically controls gear shift timing, clutch and brake hydraulic pressure and engine torque during shifting to achieve optimum shift feeling. A shift lock system is also incorporated to prevent possibility of incorrect operation of the transmission. The transmission ECM and engine control ECM are integrated.