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Making Sense of Sensors: Part 1
| There are a lot of things going on in your engine as you drive. A lot of information is taken in and processed. But how is this information gathered and what happens to it once it's collected? |
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Heated Oxygen Sensor (HO2S)
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.
Throttle Position Sensor (TPS)
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.
Vehicle Speed Sensor (VSS)
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.
Power Steering Pressure Switch (PSPS)
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.
Manifold Absolute Pressure (MAP)
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 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 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.
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