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Air flow sensor is installed in the air intake hose. Air flow sensor is composed of an
extremely small heatsensing resistor. The air flow sensor controls the amount of electric current
flowing into the heat sensing resistor to keep the heat sensing resistor at a constant temperature
to the intake air temperature. When the air mass flow rate increases, the air flow speed is
higher and also the amount of heat transfer from the heat sensing resistor to the air increased.
Therefore, the air flow sensor increases the amount of electric current to the heat sensing resistor.
Thus, the amount of electric current increases in accordance with the air mass flow rate. The
air flow sensor measures the air mass flow rate by detecting the amount of electric current.
The air flow sensor amplifies the detected electric current amount and outputs it into the engine-ECU. Engine-ECU
uses this output current and engine speed to calculate and decide basic fuel injection time.
Sensor properties are as shown in the figure.
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Intake air temperature sensor is built in to the air flow sensor. Intake air temperature
sensor detects intake air temperature through thermistor’s resistance change and outputs
the voltage according to intake air temperature to engine-ECU. Engine-ECU uses this output voltage
to compensate fuel injection control and ignition timing control. Sensor properties are as shown
in the figure.
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The manifold absolute pressure sensor is installed in the inlet manifold. Manifold absolute
pressure sensor uses a piezo resistive semiconductor to output the voltage according to manifold
absolute pressure to engine-ECU. Engine-ECU uses this output voltage to compensate fuel injection
volume according to manifold absolute pressure. Sensor properties are as shown in the figure.
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The engine coolant temperature sensor is installed in the thermostat housing. The structure
and operation is basically the same as that of the 4A91 engine. Refer to GROUP 13A - Sensor  .
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The throttle position sensor is installed in the throttle body. Throttle position sensor
outputs voltage to engine-ECU based on the throttle shaft rotation angle. Engine-ECU uses this
signal to detect the throttle valve opening angle to perform throttle valve control servo feedback
control. This throttle position sensor uses Hall IC and is a non-contact type.
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Throttle position sensor is composed of a permanent magnet fixed on the throttle shaft,
Hall IC that outputs voltage according to magnetic flux density and a stator that efficiently
introduces magnetic flux from the permanent magnet to Hall IC.
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Magnetic flux density at Hall IC is proportional to the output voltage.
Throttle position sensor has 2 output systems - throttle position sensor (main)
and throttle position sensor (sub), and the output voltage is output to engine-ECU. When throttle
valve turns, output voltage of throttle position sensor (main) and throttle position sensor
(sub) changes. This allows engine-ECU to detect actual throttle opening angle. Engine-ECU uses
this output voltage for throttle valve control servo feedback control. Also, engine-ECU compares
output voltage of the throttle position sensor (main) and throttle position sensor (sub) to check
for abnormality in the throttle position sensor. The relationship between throttle opening angle
and output voltage of the throttle position sensor (main) and throttle position sensor (sub)
is as shown in the figure below.
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The structure and operation is basically the same as that of the 4A91 engine. Refer to
GROUP 13A - Sensor .
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Oxygen sensors are installed in 2 positions (front, rear) on catalytic converter. Oxygen
sensor has a built-in heater to help early activation of the sensor. This allows feedback control
of air-fuel ratio soon after engine start.
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This sensor uses the oxygen concentration cell principle of solid electrolyte (zirconia)
and displays the property of sudden change in output voltage near theoretical air-fuel ratio.
This property is used to detect oxygen density in exhaust gas. Feedback to engine-ECU allows
it to judge whether air-fuel ratio is rich or lean compared to theoretical air-fuel ratio.
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This allows engine-ECU precise feedback control to get theoretical air-fuel ratio with
best cleaning efficiency of 3-way catalytic converter.
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A crank angle sensor is installed on the exhaust side of the cylinder block. The crank
angle sensor monitors rotation of crankshaft sensing ring (36 teeth including 3 missing teeth) installed
on the crankshaft and converts to voltage (pulse signal) that is output to engine-ECU. Engine-ECU
uses crank angle sensor’s output pulse to detect crankshaft position.
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The crank angle sensor uses a magnetic resistance element. When the vane of the crankshaft-sensing
ring passes the front surface of the magnetic resistance element, the flux from the magnet passes
the magnetic resistance element. Thus, resistance of the magnetic resistance element increases.
When the vane of the crankshaft-sensing ring does not pass the front surface of the magnetic
resistance element, the flux from the magnet does not pass the magnetic resistance element and
the resistance decreases. The crank angle sensor converts this change in resistance of the magnetic
resistance element to a 5 V pulse signal and outputs it to engine-ECU.
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The inlet camshaft position sensor is installed on the inlet side of the cylinder head.
The inlet camshaft position sensor monitors shape of the half-moon sensing portion and converts to
voltage (pulse signal) that is output to engine-ECU. Upon receiving this output voltage, the
engine-ECU effects feedback control to optimize the phase of the inlet camshaft. Also, engine-ECU
uses a combination of the camshaft position sensor output pulse signal and crankshaft position
sensor output pulse signal to identify cylinders in the compression process.
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The inlet camshaft position sensor uses a magnetic resistance element. When the camshaft
position sensing portion passes the front surface of the magnetic resistance element, the flux from
the magnet passes the magnetic resistance element. Thus, resistance of the magnetic resistance
element increases. When the camshaft position sensing portion does not pass the front surface
of the magnetic resistance element, the flux from the magnet does not pass the magnetic resistance
element and the resistance decreases. The inlet camshaft position sensor converts this change
in resistance of the magnetic resistance element to a 5 V pulse signal and outputs it to engine-ECU.
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The exhaust camshaft position sensor is installed on the exhaust side of the cylinder
head. The exhaust crankshaft position sensor monitors shape of the half-moon sensing portion
and converts to voltage (pulse signal) that is output to engine-ECU. Upon receiving this output
voltage, the engine-ECU effects feedback control to optimize the phase of the exhaust camshaft.
The structure and system of this sensor are basically the same as inlet camshaft position sensor.
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A detonation sensor is installed on the inlet side of the cylinder block. Detonation sensor
uses the piezoelectric element to convert the vibration of the cylinder block generated when engine
is in operation to minute voltage that is output to engine-ECU. Engine-ECU uses the minute output
voltage from the detonation sensor filtered through the cylinder block’s natural frequency
to detect knocking, and compensates the ignition timing lag according to the strength of the
knocking.
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A barometric pressure sensor is built into engine-ECU. The barometric pressure sensor
is a semiconductor diffused pressure element which outputs voltage to engine-ECU according to
atmospheric pressure. Engine-ECU uses this output voltage to sense the altitude of the vehicle
and compensates fuel injection volume to achieve the appropriate air-fuel ratio for that altitude.
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A vehicle speed sensor is installed on the transmission. The vehicle speed sensor uses
Hall IC. The vehicle speed sensor monitors rotation of the speedometer drive gear installed
on the differential case and converts to voltage that is output to engine-ECU. Engine-ECU calculates
vehicle speed based on the vehicle speed sensor’s output frequency. Sensor properties are
as shown in the figure.
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The structure and operation is basically the same as that of the 4A91 engine. Refer to
GROUP 13A - Sensor .
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A power steering fluid pressure switch is installed on the power steering oil pump. The
power steering fluid pressure switch uses a contact switch to detect the power steering fluid pressure.
When power steering oil pressure rises due to operation of the steering wheel, the power steering
load switch outputs an ON signal to engine-ECU. Engine-ECU performs idle-up according to the
voltage and prevents reduction in engine speed due to power steering load and so maintains stable
idle speed.
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Alternator turns ON/OFF the power transistor in the voltage regulator to adjust current
flow in the field coil according to alternator output current. In this way alternator output
voltage is kept adjusted (to about 14.4 V). The ratio of power transistor ON time (ON duty)
is output from alternator FR terminal to engine-ECU. Engine-ECU uses this signal to detect alternator output
current and drives throttle valve control servo according to output current (electric load).
This prevents change in idle speed due to electric load and helps maintain stable idle speed.
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After turning on the ignition switch, the current is input by the engine-ECU to the alternator
L terminal. This allows the voltage regulator to be on and the field coil to be excited. When
the alternator rotates in this situation, the voltage is excited in the stator coil and the
current is output from B-terminal through the commutation diode. Also the generated voltage
is input to the voltage regulator through the commutation diode. After the electric generation
begins, the current is supplied to the field coil from this circuit. In addition, the generated
voltage is output from the alternator L terminal to the engine-ECU. This allows the engine-ECU
to detect that the electric generation begins. The engine-ECU outputs the ON signal to the combination meter
through the CAN and then turns off the charge lamp.
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