« Back to Dictionary Index
A Vehicle Speed Sensor (VSS) is a component in a vehicle’s drivetrain system responsible for detecting and transmitting information about the speed of the vehicle to the electronic control module (ECM) or engine control module (ECU).
Functionality:
- Speed Detection: The VSS measures the rotational speed of a component in the drivetrain, such as the transmission output shaft, driveshaft, or wheel hub. This rotational speed correlates directly with the vehicle’s speed.
- Signal Generation: As the drivetrain component rotates, the VSS generates a signal, typically in the form of a digital pulse or analog voltage, proportional to the speed of rotation.
- Transmission to ECM: The generated signal is transmitted to the ECM or ECU, which processes the information and uses it for various functions, including engine management, transmission control, fuel injection timing, and vehicle speed display on the dashboard.
Types of VSS:
- Wheel Speed Sensors: Located near the wheels, these sensors detect the speed of individual wheels and are commonly used in anti-lock braking systems (ABS) and traction control systems (TCS).
- Transmission Output Shaft Speed Sensors: Installed on the transmission, these sensors measure the speed of the transmission output shaft, providing information about vehicle speed to the ECM.
- Driveshaft Speed Sensors: Mounted on the driveshaft, these sensors monitor the rotational speed of the driveshaft, which is directly proportional to the vehicle speed.
Importance:
- Critical Data: Vehicle speed is a crucial parameter for proper engine and transmission operation, fuel efficiency, emissions control, and the functioning of various safety systems.
- Integration with Vehicle Systems: The vehicle speed signal from the VSS is used by numerous systems within the vehicle, including the engine control system, transmission control system, cruise control system, and speedometer cluster.
Malfunction:
- Symptoms: A malfunctioning VSS can cause various issues, including inaccurate speedometer readings, erratic shifting of the transmission, and failure of cruise control systems.
- Diagnostic Trouble Codes (DTCs): When a VSS fails or malfunctions, it may trigger specific diagnostic trouble codes (DTCs) in the ECM or ECU, which can be read using a diagnostic scanner to pinpoint the issue.
In summary, the Vehicle Speed Sensor (VSS) plays a crucial role in providing accurate vehicle speed information to the electronic control module (ECM) or engine control module (ECU), enabling proper operation of various vehicle systems and ensuring optimal performance and safety.
« Back to Dictionary Index