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Your vehicle’s powertrain and cruise control rely on signals from its transmission speed sensors for functioning optimally. Should they malfunction, its powertrain control module (PCM) will set a diagnostic trouble code and illuminate its Check Engine Light on your dashboard.
These sensors play a vital role in shifting, engine calibrations and cruise control functions. If they become defective, your car could shift roughly or harshly and your cruise control may stop working as intended.
Vehicle Speed Sensor
Vehicle speed sensors (also referred to as transmission speed sensors) are vital parts of your car’s functionality, sending signals directly to both engine control modules and transmission control modules that determine how quickly your car accelerates, brakes or shifts.
Information collected is sent to an ECU that then calculates ignition timing, transmission shift points and air/fuel ratios accordingly. Cruise control uses this data to maintain a constant vehicle speed.
These sensors are made to withstand harsh environments, using high-grade materials that resist corrosion. Overexposure to elements may lead to premature failure; be sure to replace this sensor regularly to ensure its functioning correctly.
The speed sensor produces a rectangular voltage signal which is received and detected by an onboard computer to indicate vehicle speed. Often found within the tachometer or gearbox, these sensors utilize Hall Effect technology that generates electrical pulses with frequency increasing with car speed.
Faulty sensors may cause various driving-related problems that require immediate resolution, including malfunctioning speedometer, check engine light or poor shifting. If your traction control or anti-lock brake systems are also affected, their warning lights will also likely illuminate.
Faulty speed sensors can create transmission issues. Damage caused by them could wreak havoc with internal components of your transmission and lead to costly repair bills in the future.
Your mechanic should inspect the speed sensor to identify if it is malfunctioning and, if that is the case, order a replacement part for you. As speed sensors may be located in hard-to-reach spots on your vehicle, having professional inspect it may be beneficial.
Technicians use special testing equipment to measure Ohms and gather other relevant data about speed sensors. If any problems exist, technicians must quickly replace it to restore performance.
Vehicle speed sensors may be found in various locations depending on the make and model of your car. For assistance in locating its exact position, referring to your owner’s manual is often helpful.
Once the VSS has been identified, using a multimeter to check its function is easy; parking on level ground allows easier access.
Drivers should avoid operating vehicles with malfunctioning speed sensors as this can be extremely hazardous. A vehicle that lacks adequate speed regulation may make driving hazardous conditions for yourself and other motorists alike.
Contacting your local auto repair shop can help you quickly determine if a speed sensor needs replacing, by performing a comprehensive inspection to identify issues and order a new part. Their technician will then install it quickly so as to keep you safe on the roads.
Differential Speed Sensor
If your vehicle features anti-lock brakes, its differential speed sensor sends signals to the ABS control module that indicate wheel speeds on each side. The ABS module uses this information to calculate brake performance when the vehicle has stopped and when its driver selects an ABS mode.
A differential speed sensor (DSS) is a mechanical sensor found in transmissions, gearboxes, or near wheels to measure vehicle speed and send this information back to a computer. It uses variable reluctance or Hall effect signals to generate pulses that signal when wheel speed changes occur and send this data onward to your onboard engine computer, commonly referred to as an ECU (Engine Control Unit).
Differential speed sensors come in two primary varieties, reluctance and magnetoresistive. Both work by sensing rotational speed of reluctor rings before sending out square wave signals to your vehicle’s electronic control unit (ECU).
Reluctance-type sensors are common on older vehicles and feature a wide air gap between sensor and tone ring, making it more stable in high vibration conditions. Magnetoresistive types, however, tend to be smaller and can even be integrated into hub bearings using an alternating magnetic pole reluctor ring that helps the sensor function more efficiently.
If you are uncertain as to which sensors exist in your vehicle, it would be wise to contact an automotive electronics specialist for guidance. They will be able to tell you which type of sensor exists as well as its location.
Read your vehicle manufacturer’s installation instructions to identify which sensor type exists in your car and its purpose. These instructions will show where and why a particular sensor was installed in your car.
In most instances, sensors are housed within a metal cylinder located between the center of each wheel and axle shaft. The cylinder may contain a rubber seal to help keep oil from escaping when running the engine.
Sealing is of great importance as your vehicle speeds can cause oil to expand within its cylinder and cause it to rust up or even blockage which would prevent its reluctance sensor from working correctly.
One of the easiest ways to ensure that your transmission speed sensor is operating as intended is with a scan tool. Most scan tools will allow you to check each wheel speed sensor inputs and see their Performance Information Data or PID, enabling you to easily identify if there is an issue with any WSS signals being sent directly or indirectly to an ABS control module, vehicle computer or even your vehicle itself.
If your scan tool reveals any issues with any of the wheel speed sensors, it is highly advised that they be replaced immediately before your ABS system becomes compromised and could lead to skidding and other serious vehicle problems.