Car Sensors: Classification and Application

Catalog

I Development History

In the 1960s, automobiles featured only basic sensors including oil pressure sensors, fuel quantity sensors, and water temperature sensors, which were connected to simple instruments or indicator lights.

After entering the 1970s, to control emissions and meet environmental regulations, catalytic converters, electronic ignition systems, and fuel injection devices were introduced, requiring precise air-fuel ratio maintenance. This necessitated additional sensors to help control the car's powertrain system. The 1980s saw significant safety improvements with the introduction of anti-lock braking systems (ABS) and airbags.

Today, modern vehicles utilize sophisticated sensor networks for:

(1) Measuring temperature and pressure of various fluids (intake air temperature, manifold pressure, coolant temperature, fuel injection pressure, etc.)

(2) Determining wheel speed and position of various components (vehicle speed, throttle position percentage, camshaft and crankshaft positions, transmission angles and speeds, exhaust gas recirculation (EGR) valve positions, etc.)

(3) Measuring engine load, knock detection, misfire detection, and oxygen content in exhaust gases

(4) Determining seat positions and occupancy

(5) Measuring wheel speed, road surface variations, and tire pressure in anti-lock braking systems and suspension control devices

Airbags for protecting passengers require multiple impact sensors and acceleration sensors. Modern anti-collision systems use radar, lidar, or camera-based sensors to determine and control lateral acceleration, instantaneous speed of each wheel, and required torque, making the braking system an integral part of vehicle stability control systems.

Modern airbag system with multiple sensors

Traditional oil pressure and water temperature sensors operated independently with clear maximum or minimum limits. As sensors evolve toward electronic and digital systems, their output values are utilized more comprehensively, with many modern automotive sensors functioning as intelligent switches with variable output capabilities.

II Classification and Application

Types of Sensors in Modern Cars

Sensors for engine control systems form the core of automotive sensor networks, including temperature sensors, pressure sensors, position and speed sensors, flow sensors, gas sensors, and knock sensors. These automotive sensors provide precise control of engine operating conditions for the Electronic Control Unit (ECU) to optimize dynamic performance, reduce fuel consumption and exhaust emissions, and perform comprehensive fault detection.

Modern automotive ECU with sensor connections

1. Temperature Sensors

Automotive temperature sensors are primarily used to detect engine temperature, intake air temperature, coolant temperature, fuel temperature, and catalytic converter temperature. There are three main types of vehicle temperature sensors: wire-wound resistor type, thermistor type, and thermocouple type. Each type has distinct characteristics and specific applications.

(1) Wire-wound resistor temperature sensors offer high accuracy but have poor response characteristics.

(2) Thermistor temperature sensors provide high sensitivity and good response characteristics but have poor linearity and are better adapted to lower temperatures.

(3) Thermocouple temperature sensors offer high accuracy and wide temperature measurement ranges but require amplifiers and cold-junction compensation.

Car coolant temperature sensor

2. Pressure Sensors

Automotive pressure sensors are primarily used to detect cylinder vacuum, atmospheric pressure, turbocharger boost pressure, cylinder internal pressure, and oil pressure. Intake manifold pressure sensors are mainly used for detecting intake air pressure, vacuum levels, and oil pressure. There are numerous types of pressure sensors used in automobiles: capacitive, piezoresistive, linear variable differential transformer (LVDT), and surface acoustic wave (SAW) types.

(1) Capacitive pressure sensors are primarily used to detect vacuum, hydraulic pressure, and air pressure, measuring ranges from 20-100kPa, with high input energy, excellent dynamic response characteristics, and good environmental adaptability.

(2) Piezoresistive pressure sensors are significantly affected by temperature, often requiring separate temperature compensation circuits, but are suitable for mass production.

(3) LVDT pressure sensors have large output signals and are easy to digitize, but have poor interference resistance.

(4) SAW pressure sensors feature small size, lightweight construction, low power consumption, high reliability, sensitivity, and resolution, used to detect intake manifold pressure and capable of stable operation at high temperatures.

Automotive pressure sensor applications

3. Flow Sensors

Flow sensors are primarily used for measuring engine airflow and fuel flow. Airflow measurement is used by engine control systems to determine combustion conditions, control air-fuel ratios, startup procedures, ignition timing, etc. There are four types of airflow sensors: rotary vane type, Karman vortex type, hot wire type, and hot-film type.

(1) Rotary vane airflow sensors have simple structures and lower measurement accuracy. The measured flow requires temperature compensation.

(2) Karman vortex airflow sensors have no moving parts, are sensitive, and require high accuracy with temperature compensation.

(3) Hot-wire airflow sensors have high measurement accuracy with no temperature compensation required, but are easily affected by gas pulsation and prone to breakage.

(4) Hot-film airflow sensors use the same measuring principle as hot-wire sensors but are smaller in volume and suitable for mass production at lower cost.

Main technical specifications of airflow sensors:

• Working range: 0.11-103 m³/min

• Operating temperature: -40°C to 120°C

• Accuracy: ≤ 1%

(5) Fuel flow sensors are used to detect fuel flow, mainly divided into turbine wheel type and circulating ball type.

Technical specifications:

• Dynamic range: 0-60kg/h

• Operating temperature: -40°C to 120°C

• Accuracy: 1%

• Response time:<10ms

Mass airflow sensor

4. Position and Speed Sensors

Position and speed sensors are primarily used to detect crank angle, engine speed, throttle position percentage, vehicle speed, etc. Automotive position sensors and speed sensors include generator type, magnetoresistive type, Hall effect type, reed switch type, optical type, semiconductor magnetic transistor type, etc. The measurement range is 0-360°, with accuracy better than 0.5°, and measured angle resolution of 0.1°.

There are many types of vehicle speed sensors, including those sensitive to wheel rotation, transmission rotation, and differential drive shaft rotation. When vehicle speed exceeds 100km/h, conventional measurement methods have significant errors, requiring non-contact photoelectric speed sensors.

Technical specifications:

• Speed range: 0.5-250km/h

• Repeat accuracy: 0.1%

• Distance measurement error:<0.3%

Hall effect sensors in automotive applications

5. Gas Sensors

Gas sensors are primarily used to detect exhaust gas composition and emissions in vehicles. The most important is the automotive oxygen sensor. Practical types include zirconia sensors (operating temperature -40°C to 900°C, accuracy 1%), zirconia concentration cell gas sensors (operating temperature 300°C to 800°C), solid electrolyte zirconia gas sensors (operating temperature 0°C to 400°C, accuracy 0.5%), and titanium dioxide automotive O₂ sensors. Compared to zirconia sensors, titanium dioxide oxygen sensors have simpler structures, are lightweight, cost-effective, and have strong resistance to lead contamination.

Automotive gas sensor

6. Knock Sensors

Automotive knock sensors, also called vibration sensors, are used to detect engine oscillation by adjusting ignition advance angle to control and prevent engine knock. Knock detection can be achieved by testing cylinder pressure, engine block vibration, and combustion noise.

Knock sensors include magnetostrictive and piezoelectric types. The magnetostrictive knock sensor operates at temperatures from -40°C to 125°C with a frequency range of 5-10kHz. Piezoelectric knock sensors have sensitivity up to 200mV/g at center frequency of 5.417kHz and exhibit good linearity at amplitudes of 0.1g-10g.

Knock sensor

7. Radar Sensors

Modern automotive radar systems utilize multiple frequency bands: 24GHz, 77GHz, and 79GHz radar sensors are used in collision avoidance systems, adaptive cruise control, and autonomous driving features. These systems emit radar waves to determine object size, distance, and movement speed to prevent collisions using display systems and automated braking. The 77GHz band is now preferred for long-range applications due to better resolution and smaller antenna size requirements.

Automotive radar sensor

8. Vehicle Body Control Sensors

Vehicle body control sensors are primarily used to improve automotive safety, reliability, and comfort. Since their operating conditions are less harsh than engine sensors and chassis components, general industrial sensors can be applied with minor modifications. These automotive sensors can be categorized into several groups according to their applications:

(1) Automatic climate control systems: temperature sensors, humidity sensors, air volume sensors, and sunlight sensors

(2) Airbag systems: acceleration sensors and impact sensors

(3) Door lock control: vehicle speed sensors

(4) Automatic brightness control: ambient light sensors

(5) Parking assistance: ultrasonic or laser sensors

(6) Safe following distance: distance sensors

(7) Blind spot elimination: camera and image sensors

(8) Navigation systems: compass sensors, gyroscopes, vehicle speed sensors, and steering wheel angle sensors

Additional sensors used in vehicle body applications include: collision acceleration sensors, ultrasonic short-range sensors, infrared sensors, millimeter-wave radar, and ambient gas electrochemical sensors. Advanced sensor types include reverse sensors, lane departure warning systems, and infrared thermal imaging night vision sensors.

9. Car Sensors for Chassis Applications

(1) Transmission control systems: vehicle speed sensors, accelerator pedal position sensors, acceleration sensors, throttle position sensors, engine speed sensors, coolant temperature sensors, transmission fluid temperature sensors, etc.

(2) Suspension control systems: vehicle speed sensors, throttle sensors, acceleration sensors, body height sensors, steering wheel angle sensors, etc.

(3) Power steering systems: vehicle speed sensors, engine speed sensors, torque sensors, hydraulic pressure sensors, etc.

Digital chassis acceleration sensors

III Detection of Car Sensors

(Using throttle position sensor as the discussion example)

The driver operates the vehicle throttle with the accelerator pedal to change engine air intake, thereby controlling engine operation. Different throttle positions indicate various engine operating conditions.

1. Detection of the Throttle Switch

(1) Structure and Circuit

The throttle switch, also called switch output type throttle position sensor, has two pairs of contacts: idle contact (IDL) and full load contact (PSW). A cam coaxial with the throttle valve controls the opening and closing of these switch contacts.

Throttle position sensor structure

When the throttle valve is fully closed, the idle contact closes, and the ECU determines that the engine is in idle mode according to the idle switch closing signal, controlling fuel injection quantity according to idle mode requirements.

When the throttle valve opens, the idle contact opens, and the ECU performs fuel injection control during the transition from idle to light load based on this signal. The full load contact remains open from fully closed to small and medium throttle openings.

When the throttle opens to a certain angle, the full-load contact closes, sending a signal to the ECU that the engine is in full-load operation, and the ECU performs full-load enrichment control based on this signal.

(2) Check and Adjustment

• Check conductivity between terminals in the vehicle

Step 1: Set the ignition switch to "OFF" position, remove the throttle position sensor connector, and insert an appropriate thickness gauge between the throttle stop screw and limit rod.

Step 2: Connect a multimeter to the connector to test the conduction mode of idle contacts and full load contacts.

When the throttle is fully closed, the idle contact should be conducting; when the throttle is fully opened or nearly fully opened, the full load contact should be conducting; at other opening angles, neither contact should be conducting. The specific conditions are shown in Table 1. Otherwise, the throttle position sensor should be adjusted or replaced.

Table 1. Throttle switch contact states

2. Detection of Throttle Valve with Linear Variable Resistance Output

(1) Structure and Circuit

The throttle position sensor with linear variable resistance output is a type of linear potentiometer whose sliding contact is driven by the throttle shaft. Under different throttle positions, the potentiometer resistance varies, converting throttle position into voltage signals sent to the ECU. Through the throttle position sensor, the ECU obtains continuously changing voltage signals representing all throttle valve opening angles and the rate of throttle position change, enabling more accurate determination of engine operating conditions. Generally, this type of throttle position sensor also includes an idle contact (IDL) to determine engine idle operating conditions.

(2) Inspection and Adjustment

• Conductivity Detection of Idle Contact

• Set the ignition switch to "OFF" position, remove the throttle position sensor wire connector, and use a multimeter to measure idle contact conductivity on the connector. When the throttle is fully closed, resistance between terminal IDL and E2 should be 0Ω. When the throttle is open, resistance between the two terminals should be ∞. Otherwise, replace the throttle position sensor.

• Measure the resistance

Set the ignition switch to OFF position, unplug the throttle position sensor wire connector, and measure the linear potentiometer resistance with the multimeter's Ω setting. The resistance should increase linearly with increasing throttle position.

IV Development Trend of Car Sensors

The development trend of automotive sensor technology is toward miniaturization, multi-functionality, integration, and intelligentization.

Currently, advancements in design technology, materials technology, especially MEMS (Microelectromechanical Systems) technology, have brought micro-sensors to new levels. Using microelectronic mechanical processing technology, micron-level sensitive components, signal processors, and data processing devices can be packaged on a single chip, featuring small size, low cost, high reliability, and significantly improved system test accuracy. Additionally, MEMS technology enables manufacturing of miniature sensors that detect mechanical, magnetic, thermal, chemical, and biological quantities. Because MEMS miniature sensors can greatly reduce automotive electronic system costs while improving performance, they are gradually replacing sensors based on traditional electromechanical technology and becoming an important component of global automotive electronics.

MEMS automotive sensors offer low cost, excellent reliability, and small size. They can be integrated into new systems and operate for millions of hours. The earliest MEMS devices were absolute pressure sensors and airbag acceleration sensors. Currently, MEMS/MST products under development and in small-batch production include wheel speed rotation sensors, tire pressure sensors, refrigeration pressure sensors, engine oil pressure sensors, brake sensors, and yaw rate sensors. In the next 5-7 years, MEMS devices will be widely adopted in automotive systems.

With microelectronic technology development and rapid increase in automotive electronic control system applications, market demand for automotive sensors will maintain rapid growth. Miniaturized, multifunctional, integrated, and intelligent sensors based on MEMS technology will gradually replace traditional sensors and become mainstream automotive sensors.

• Multifunctionality means one sensor can detect two or more physical or chemical parameters, reducing the number of vehicle sensors and improving automotive sensor system reliability.

• Integration refers to using IC manufacturing technology and precision processing technology to create IC-type sensors.

• Intelligentization refers to combining sensors with large-scale integrated circuits containing CPUs, providing intelligent functions to reduce ECU complexity, volume, and costs.

MEMS automotive sensors

Article Update Information

Last Updated: October 2025

Key Updates Made:

• Updated radar sensor frequencies to include modern 77GHz and 79GHz systems

• Enhanced mobile-responsive design with modern CSS styling

• Corrected technical specifications and temperature ranges

• Added information about autonomous driving sensor technologies

• Updated MEMS technology applications and market trends

• Expanded coverage of advanced driver assistance systems (ADAS)

• Added current automotive sensor integration examples

• Improved technical accuracy of sensor detection procedures

• Updated recommended articles section

Technology Evolution Since 2020: Automotive sensors have significantly advanced with AI integration, enhanced ADAS capabilities, electric vehicle-specific sensors, and improved connectivity for autonomous driving applications. The market has expanded dramatically with the rise of electric vehicles and autonomous driving technologies.

Recommended Articles:

What are Types and Application of Gas Sensors?            Working Principle and Application of Infrared Sensors            All You Need to Know about Ultrasonic Sensors            Introduction to Temperature Sensors