A vehicle’s speed sensor is a critical component that allows the engine control unit (ECU) to determine the speed at which the vehicle is traveling. This information is used for various essential functions like cruise control, anti-lock brakes, traction control, and more. While speed sensors are generally durable, there are some potential causes of damage that can lead to speed sensor failure.
Mechanical Damage
One of the most common ways a speed sensor can become damaged is through physical impact or abrasion. Speed sensors are located near the vehicle’s wheels and drivetrain components, making them vulnerable to road debris, potholes, curbs, or other objects on the road. A strong impact near the speed sensor location can bend, crack, or break the sensor. Even grazing the sensor along the ground at high speeds can wear away the protective cover and expose the internal sensing components.
In rear-wheel drive vehicles, the speed sensor is located inside the rear axle or differential. Heavy impacts to the rear suspension or axle components can transfer damaging forces directly to the sensor. Front-wheel drive speed sensors are housed inside the transmission or transaxle, providing some protection, but hard jolts from potholes or debris can still cause harm.
Speed sensors are also positioned very close to constantly moving parts like brake rotors, CV joints, and wheel bearings. If any of these components become worn or damaged, they can throw off debris that abrades the sensor tip. Metal shavings from a worn bearing or broken gear tooth can quickly grind away the speed sensor and lead to failure.
Mechanical Damage Prevention
- Avoid potholes, curbs, and road debris when possible
- Inspect and replace worn drivetrain components like CV joints
- Check wheel bearings and differentials for excess play and debris
- Replace bent or cracked sensor mounts that expose the sensor
Electrical Damage
Along with mechanical harm, speed sensors can also be damaged by electrical issues in the vehicle. Problems like shorts, surges, and overvoltage can burn out the sensitive electronic components inside the sensor. Damaged wiring insulation, pinched wires, and loose connectors are common causes of electrical faults that can fry a speed sensor.
Short circuits are particularly hazardous because they can send an uncontrolled power spike through the sensor. This rapid influx of current overwhelms the small integrated circuits and resistors inside the speed sensor, causing irreversible damage. It only takes a split second of excess current to burn out the internal components and render the sensor unusable.
Electrical surges can also be produced by aftermarket devices like high-powered stereo systems, off-road lights, or auxiliary power outlets. Connecting these accessories directly to the existing wiring harness adds additional load to the system. The surge when turning on high-draw devices can travel back through the speed sensor circuit and blow out the electronics.
Electrical Damage Prevention
- Fix damaged wiring insulation and frayed wires
- Ensure good pin contact in connectors and avoid corrosion
- Use proper size fuses to protect sensor circuits
- Isolate aftermarket accessories with relays and separate fusing
Contamination
Environmental contaminants are another potential cause of speed sensor malfunction. Road salt, dirt, and water can all work their way into the sensor housing and interfere with operation. Heavy accumulations of mud or debris around the sensor tip can physically block it from reading the metallic reluctor teeth passing by.
Liquid contamination is especially detrimental if it manages to get inside the electronic housing. Minerals in the water or road salt can leave conductive deposits that short out the circuit board and internal components. This leads to sensor failure as the contamination builds up over time.
Oil leaks from worn engine seals can also foul the sensor tip and prevent it from accurately reading wheel speed. The thick oil causes asphalt buildup on the end of the sensor, masking the reluctor signal. Some synthetic gear oils can also degrade the plastic components of the sensor housing.
Contamination Prevention
- Fix leaks from oil seals, axles, and CV joints
- Inspect wiring and housing for proper sealing
- Clean sensors and wiring to remove mud or debris buildup
- Avoid aiming pressure washers directly at sensors
Improper Handling
One of the easiest ways that technicians damage speed sensors is through careless handling when working in tight quarters around the brakes, bearings, or transmission. It’s easy to bump or apply excessive force to the sensor tip when trying to remove other components for service.
Twisting or bending the sensor tip out of alignment can damage the internal sensing element. The sensor is only designed to move in a very narrow range of motion. Technicians also need to be extremely careful not to shear off the mounting pins or electrical connector during removal. Once disconnected from the wiring, a speed sensor is very vulnerable to being dropped or stepped on.
Sensor Handling Best Practices
- Avoid bending, twisting, or impacting the sensor tip
- Use proper tools to detach sensor mounts and connectors
- Carefully support sensor during removal to avoid dropping
- Cover and protect disconnected sensors from damage
- Follow manufacturer test procedures to confirm operation
Incorrect Installation
Even a brand new speed sensor won’t function properly if it gets damaged during installation. Rushing the job or using inferior parts can easily ruin a new sensor and lead to premature failure. Applying too much force when installing the sensor can physically damage the tip or twist the housing out of alignment.
Using the wrong type of thread locker compound is another common mistake. Some low quality or high-strength thread lockers contain solvents that can interact with plastic sensor housings and cause them to crack. Always follow the vehicle manufacturer specifications for proper thread locking procedures.
Failing to attach the sensor wiring connector properly or leaving the lock tab open also leads to installation errors. This causes intermittent contact that sends wrong signals to the ECU, or allows moisture and debris into the connectors. Taking the time to fully seat connectors and positively lock them prevents sensor damage.
Proper Sensor Installation
- Follow torque specifications for mounts
- Use OEM-approved thread locker
- Ensure full, locked connection of harness plug
- Confirm proper air gap specs for sensors
- Test operation before reassembly
Incompatible Replacement Parts
One of the most common DIY mistakes when repairing a bad speed sensor is using an aftermarket replacement part that doesn’t match the OEM spec. Generic sensors from parts stores often have different connector styles, tip sizes, output voltages, or detection ranges. Installing an incompatible sensor almost guarantees incorrect speed readings and sensor codes.
Even similar looking aftermarket sensors can have internal component variances that lead to premature failure. And cheap direct replacement sensors rarely last as long as the factory parts from vehicle manufacturers. It might seem cheaper up front, but you’ll end up doing the repair again after the sensor fails in short order.
Aftermarket speed sensors also regularly have fitment issues that require modification or force to install correctly. This often damages the new sensor right from the start. For maximum durability and proper operation, always replace failed speed sensors with OEM parts from the vehicle maker.
Speed Sensor Selection Tips
- Compare aftermarket options to OEM sensor specs
- Verify connector style, tip size, and air gap
- Check output voltage range and sensing accuracy
- Buy from a reputable source with strict quality control
- Pay extra for factory sensors when possible
Conclusion
Speed sensors play a vital role in proper vehicle operation, but are susceptible to many different types of damage. Physical harm, electrical issues, contamination, mishandling, and improper installation can all cut short the normal life span of a vehicle speed sensor. Being aware of the potential failure causes and taking steps to prevent them will maximize the durability of these critical engine management components.
When issues do occur, use OEM-grade replacement parts from reputable suppliers, and follow all manufacturer service procedures closely. With diligent prevention and proper repair, speed sensor problems don’t have to halt your travels.