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Essential Engine Sensors for Vehicle Efficiency

By R&D
Published on June 26th, 2024

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Your vehicle's computer control system receives information from a variety of sensors. It uses this information to control engine operation for optimum performance, and to minimize emissions. When these sensor malfunction, vehicle performance is affected. Following are descriptions of the basic engine sensors in use today.

Air Temperature Sensor


The air temperature sensor is used to monitor intake air temperature. This information is used by the vehicle’s computer to make adjustments to the air/fuel ratio during engine warm-up, or in response to changes in air density. Specific applications of the air temperature sensor vary between vehicle manufacturers.

Barometric Pressure (BARO) Sensor


The barometric pressure (BARO) sensor sends a voltage or frequency signal representing atmospheric pressure to the vehicle’s computer. The level of the signal increases as atmospheric pressure increases. The vehicle’s computer uses this information to adjust air/fuel ratio and ignition timing to compensate for changes in atmospheric pressure.

Coolant Temperature Sensor (CTS)


The coolant temperature sensor (CTS) sensor monitors engine coolant temperature. Sensor resistance decreases as coolant temperature increases. The vehicle’s computer uses this information to determine when the engine is warm enough to go into closed loop feedback fuel control. The computer also adjusts air/fuel ratio, timing, idle speed, and EGR valve operation based on changes in engine temperature.

Crankshaft / Camshaft Positon Sensors


These sensors monitor the speed of the crankshaft or camshaft, and generate a series of high- and low-voltage pulses, which represent the speed of rotation, to the vehicle’s computer. The frequency of voltage pulses increases as crankshaft/camshaft rpm increases. The computer uses these signals for spark timing or fuel injector control.

EGR Valve Position (EVP) Sensor


The EGR Valve Position (EVP) Sensor is used on most Ford vehicles equipped with EEC-IV Electronic Engine Control systems to monitor the position of the EGR valve. The computer uses this information to determine the correct exhaust recirculation flow rate to effectively reduce NOX emissions.

Knock Sensor


The knock sensor detects engine vibrations caused by “knocking” (cylinder detonation), and converts the vibrations into an AC signal that is sent to the vehicle’s computer system. The computer then momentarily retards spark timing to eliminate the knock condition. Once the knocking stops, spark timing returns to normal.

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Manifold Absolute Pressure (MAP) Sensor


The manifold absolute pressure (MAP) sensor sends a voltage or frequency signal representing engine (intake) vacuum to the vehicle’s computer. The voltage or frequency increases as engine vacuum decreases. The computer adjusts air/fuel ratio and ignition timing according to changes in engine vacuum. For vehicles that use a "speed density" type of fuel injection, the vehicle’s computer also uses the MAP sensor signal as an aid in estimating airflow.

Mass Air FLow (MAF) Sensor


The mass air flow (MAF) sensor is used on fuel-injected engines. The sensor sends a voltage or frequency signal representing the quantity of air entering the engine to the vehicle’s computer. The voltage or frequency increases when air flow increases. The computer uses this signal to adjust air/fuel ratio and ignition timing based on incoming air flow. Contamination of the sensing element can result in numerous drivability problems.

Oxygen (O2) Sensor


The oxygen (O2) is the principal sensor in the fuel mixture feedback control loop. The sensor monitors the vehicle’s exhaust and sends a voltage signal representing the amount of unburned oxygen in the exhaust to the vehicle’s computer. The computer increases fuel delivery for “lean” exhaust conditions (too much oxygen) and decreases fuel delivery for “rich” exhaust conditions (too little oxygen) in order to achieve the lowest possible vehicle emissions. Aged or contaminated sensors can contribute to “rich” exhaust conditions, decreased fuel economy and increased vehicle emissions.

Throttle Position Sensor (TPS)


The throttle position sensor (TPS) is a resistance-type sensor. The sensor’s potentiometer is connected to the vehicle’s throttle. The sensor sends a voltage signal to the vehicle’s computer to indicate throttle position. The voltage increases as the throttle is opened. The computer adjusts air/fuel ratio, spark advance, and idle speed based on throttle position. The sensor actuator may be a rotary actuator (for fuel injected engines) or linear (push) actuator (for carbureted engines). Some vehicles may also employ a separate idle switch and/or wide open throttle (WOT) switch that operates in conjunction with the throttle position sensor.

Vehicle Speed Sensor (VSS)


Vehicle speed sensors (VSS) are used in late model vehicles to monitors vehicle speed. Depending on make and model, the vehicle’s computer uses this information for a number of purposes, including: torque converter clutch lockup, emission control functions, power steering assist, electronically adjustable shock control, etc. In some applications, the vehicle speed sensor replaces the mechanical speedometer cable as a means of providing input to an electronic speedometer or electronic cruise control system.

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