ECU Input Sensors
Mass Air Flow Sensor (MAF) Camshaft (or Crankshaft) Position Sensor (CPS) Coolant Temperature Sensor (CTS) Knock Sensor Heated Oxygen Sensor (HO2S) Throttle Position Sensor (TPS) Vehicle Speed Sensor (VSS) Power Steering Pressure Switch (PSPS) Manifold Absolute Pressure (MAP) The higher the MAP voltage output the lower the engine vacuum, which requires more fuel. The lower the MAP voltage output the higher the engine vacuum, which requires less fuel. Under certain conditions, the MAP sensor is also used to measure barometric pressure. This allows the computer to automatically adjust for different altitudes. The computer uses the MAP sensor to control fuel delivery and ignition timing. Cranking Signal
The mass airflow sensor is placed in the stream of intake air. It measures the intake flow rate by measuring a part of the entire intake flow. It consists of a hot wire that is supplied with electric current from the ECM. The temperature of the hot wire is controlled by the ECM a certain amount. The heat generated by the hot wire is reduced as the intake air flows around it. The more air, the greater the heat loss. Therefore, the ECM must supply more electric current to maintain the temperature of the hot wire as airflow increases. The ECM detects the airflow by means of this current change.
Intake Air Temperature sensor (IAT)
The intake air temperature sensor is mounted to the air duct housing. The sensor detects intake air temperature and transmits a signal to the ECM.
The temperature-sensing unit uses a thermistor that is sensitive to the change in temperature. Electrical resistance of the thermistor decreases in response to the temperature rise.
The camshaft position sensor monitors engine speed and piston position. These input signals to the ECM are used to control fuel injection, ignition timing and other functions. The camshaft position sensor has a rotor plate and a wave-forming circuit. The rotor plate has 360 slits for a 1°(POS) signal and 6 slits for a 120°(REF) signal. The wave-forming circuit consists of Light Emitting Diodes (LED) and photo diodes. The rotor plate is positioned between the LED and the photo diode. The LED transmits light to the photo diode. As the rotor plate turns, the slits cut the light to generate rough-shaped pulses. These pulses are converted into on-off signals by the wave-forming circuit and sent to the ECM.
The engine coolant temperature sensor is used to detect the engine coolant temperature. The sensor modifies a voltage signal from the ECM. The modified signal returns to the ECM as the engine coolant temperature input. The sensor uses a thermistor that is sensitive to the change in temperature. The electrical resistance of the thermistor decreases as temperature increases.
The knock sensor is attached to the cylinder block. It senses engine knocking using a piezoelectric element. A knocking vibration from the cylinder block is sensed as vibrational pressure. This pressure is converted into a voltage signal and sent to the ECM.
The HO2S is placed into the exhaust manifold. It detects the amount of oxygen in the exhaust gas compared to the outside air. The sensor has a closed-end tube made of ceramic zirconia. The zirconia generates voltage from approximately 1V in richer conditions to 0V in leaner conditions. The sensor signal is sent to the ECM. The ECM adjusts the injection pulse duration to achieve the ideal air-fuel ratio. The ideal air-fuel ratio occurs near the radical change from 1V to 0V.
The throttle position sensor responds to the accelerator pedal movement. This sensor is a kind of potentiometer that transforms the throttle position into output voltage, and emits the voltage signal to the ECM.
In addition, the sensor detects the opening and closing speed of the throttle valve and feeds the voltage signal to the ECM.
The ECM receiving the signal from the throttle position sensor determines idle position of the throttle valve. This sensor controls engine operation such as fuel cut. On the other hand, the "Wide open and closed throttle position switch", which is built into the throttle position sensor unit, is not used for engine control.
The vehicle speed sensor is installed in the transaxle. It contains a pulse generator that provides a vehicle speed signal to the speedometer. The speedometer then sends a signal to the ECM.
The power steering oil pressure switch is attached to the power steering high-pressure tube and detects a power steering load. When a power steering load is detected, it signals the ECM. The ECM adjusts the idle speed for the increased load.
The Manifold Absolute Pressure sensor measures changes in the intake manifold pressure resulting from engine load and speed changes. The computer sends a 5-volt reference signal to the MAP sensor.
As pressure changes in the intake manifold occur, the electrical resistance of the MAP sensor also changes. By monitoring the sensor output voltage, the computer can determine the manifold absolute pressure.
The control module uses this signal to tell when the vehicle is in the STARTING mode. This information is used to allow enrichment and cancel diagnostics while engine is cranking.
