A speed sensor essentially lets you know how fast you are driving. It helps you monitor the transmission system, wheel speed, and other important speed elements in your car.
To say that the speed sensor is vital to your car’s overall performance is an understatement. Keep reading to learn why you should not drive without a functioning speed sensor.
What does a transmission speed sensor do?
A transmission speed sensor calculates the transmission gear ratio when in use. A car has two-speed sensors: the ISS and the OSS, working together to show the transmission data to the car’s powertrain module. The ISS sensor monitors the input shaft’s speed.
The transmission speed sensors are used to calculate the actual gear ratio of the transmission while in use. Generally, two-speed sensors work in conjunction to provide accurate transmission data to the vehicle’s powertrain control module. The first is known as the input shaft speed (ISS) sensor.
The sensor is used to monitor the transmission’s input shaft speed. The other sensor is the output shaft speed (OSS) sensor. If either of these two sensors falls out of alignment or experiences electrical issues, it impacts the operation of the entire transmission.
What does a vehicle speed sensor do?
A vehicle speed sensor (VSS) is a small component mounted on your car’s transmission that lets the car’s onboard computer know how fast you’re moving. It’s also known as a wheel speed sensor, transmission speed sensor, or output shaft speed sensor.
The vehicle speed sensor measures the rotational speed of the gears in your transmission system. Then, it converts this measurement into an analog signal or a low voltage square wave signal and relays it to electronic control units (ECUs) inside your car.
What happens if a speed sensor goes bad? Symptoms of a bad speed sensor
Below are some symptoms of a damaged sensor;
Vehicle speed sensor
1. Inconsistent Speedometer Readings
Most cars depend on signals from the wheel speed sensor to adjust their speedometer readings. A faulty sensor can result in inconsistent or erratic speedometer readings.
2. The Check Engine Light Gets Activated
A faulty vehicle speed sensor can trigger the Check Engine Light. However, since many other problems can light up the MIL, you will need a scanner to pull out the error codes and figure out what specific problem your PCM found in the system.
If the VSS is the problem, expect the P0500 error code that stands for ‘Vehicle Speed Sensor malfunction.’
ProTip: If the OBDII scanner picks up other error codes, have them looked into. They could be side effects of the VSS malfunction or a totally different problem with your vehicle
3. Malfunctioning Cruise Control
In most cars, the cruise control system depends on input signals from the transmission speed sensor. The powertrain control module (PCM) inside your car automatically disables cruise control when it fails to receive a proper signal from the VSS.
4. Harsh Transmission Shifting
Without a reliable signal from the transmission speed sensor, the powertrain control module can’t correctly shift the gears within your transmission system.
If your car uses an automatic transmission system, a faulty sensor can also cause severe damage to the mechanical gear tooth profile. And other internal components like hydraulic lines, valve bodies, and more.
Transmission speed sensor
1. Harsh or Improper Shifting
Without a valid speed signal from these sensors, the PCM will not be able to control the shifting of gears within the transmission correctly. This may cause the transmission to shift roughly or more quickly than normal.
It’s also common that a problem with these sensors can impact the shift timing, extending the interval between transmission shifts.
2. Cruise Control Does Not Work
Since the transmission speed sensors monitor the input and output shaft speed, it also monitors the cruise control.
When the sensors fail to deliver accurate data to the onboard computer on your car, truck, or SUV, the powertrain control module (PCM) will send an error code to the vehicle’s ECU. As a result, the ECU will shut down the cruise control and render it inactive.
3. Check Engine Light Comes On
If the signals are lost from the transmission speed sensors, the PCM will set a DTC and illuminate the Check Engine Light on the vehicle dashboard.
It also can indicate an increase in tailpipe emissions surpassing acceptable limits for environmental contaminants from motor vehicles.
How to test a transmission speed sensor
Follow these simple steps to test a speed sensor;
- Park your vehicle on a level surface to easily access the sensor.
- Turn the vehicle off and any lights or anything that might draw power from the battery.
- To make sure that the vehicle is completely turned off, remove the key from the ignition.
- Open your vehicle’s hood and find the speed sensor located near the vehicle’s transmission.
- You can find the transmission by looking for its dipstick and following it.
- You should find a small metal sensor connected by two wires, white and black, to the transmission, which is held in place by a metal bracket.
- Vehicle speed sensor locations can vary from car to car, but they can usually be found on or next to the transmission.
- If you can’t seem to find it, check your owner’s manual to find its exact location.
- The black and white wires are connected to the speed sensor.
- One is to ground the sensor, while the other is used to send data or signals to the car’s computer.
- You need to unplug the wires from the sensor to remove them.
- You can use a small pair of pliers to remove the wires if you can’t grip them with your fingers.
- A sliding tab or a button can be found on the top or side of the speed sensor.
- Press the pull tab or button and pull the sensor gently to remove it from its housing.
- You might need to wiggle or slide it out from its base but do not force the sensor since you could damage it.
- Check if the speed sensor has screws that you need to unscrew to remove it.
- Unscrew the bolt and the bracket so you can remove the speed sensor.
- Keep the screws or bolts and ensure that you don’t lose them.
- Get your multimeter, plug the black lead into the black terminal, and insert the red lead into the red terminal with the letter “V.”
- Gently push the leads into the slots until they “click” into place.
- Set your multimeter to AC or alternating current by turning its dial.
- The speed sensor has a slot where it plugs into the vehicle.
- You need to find a plug that fits into the sensor.
- You can purchase this wire from an auto supply shop. It has a black ground wire and a white signal output wire.
- You need to plug these wires securely into the speed sensor.
- Get the black lead wire and fasten it to the exposed wire at the end of the black wire, which is plugged into the sensor.
- Connect the red lead wire to the exposed end of the white wire, which is also plugged into the sensor.
- Since you are testing a speed sensor, you need to simulate the movement to test it properly.
- You need to find a drill bit that can fit into the sensor securely to rotate the gear inside it.
- Put the drill bits into the sensor’s gear slot until you find the one that fits perfectly into the slot.
- Connect the bit to the power drill and tug it gently to ensure it won’t fall.
- Spin the sensor gears using the drill. Allow it to spin at full speed to get an accurate reading.
- You can start slowly, increasing the speed at a consistent pace.
- While the sensor spins, read the multimeter and check if the number increases with speed.
- The sensor is faulty when the voltage does not increase with speed or if it doesn’t show any voltage at all.
- You will need to replace your sensor to fix the speed sensor problems.
- Reinstall the speed sensor into your vehicle.
- If it needs replacement, make sure that you replace it with the same make and model to ensure that it will fit.
Can a bad speed sensor cause stalling and loss of power?
Yes. A damaged full sensor can cause your car to idle or rumble irregularly when you start it, or it may burn more fuel than normal when you start it. A faulty speed sensor may also cause your vehicle to lose power suddenly.
How long can you drive a car with a bad speed sensor
You should never drive your car if it has a damaged speed sensor. Driving a car with a bad speed sensor is dangerous and not advisable. You risk crashing if you do not know how fast you are driving. More so, speed sensors are inexpensive to replace.
What damages speed sensors?
These are the main causes of speed sensor damage;
Internal electrical fault
Over time, the speed sensors can get internal electrical damage. This could result in having an abnormal output signal or having no signal at all. Power surges and faulty grounding could also lead to VSS and other sensor damages.
Normal wear and tear
The sensor itself can become damaged or cracked. Its plastic part can also become brittle after being exposed to the elements. The speed sensor’s magnetic part can eventually become worn or damaged.
Poor car care and maintenance
Experts always say that proper car care and maintenance can extend the lifespan of the vehicle and its components. Following the recommended maintenance schedule can also help prolong the speed sensor’s life.
Failing to do so can increase the risk of speed sensor failure causing your vehicle to experience speed sensor problems. In addition, the sensors will not be able to give accurate readings if their parts become covered in gunk, dirt, and other fluid contaminants.
Broken wirings and loose connections.
Disconnection of the sensor to the engine control unit can cause problems too. Make sure that you check the connections for loose or broken ones. Check also for corrosions and build-up.
An internal electrical fault in the speed sensor
A speed sensor damaged internally can result in an abnormal output signal or no signal at all. Typically, the sensor can be tested with a digital voltmeter or oscilloscope.
Seek the help of a trusted mechanic if you suspect that you have a faulty VSS so it can be tested—and replaced if needed.
Damage to the sensor itself
The speed sensor can get damaged or cracked. Also, the plastic portion of the sensor can become brittle after prolonged exposure to the elements.
The magnetic portion of the sensor may also become worn and damaged over time. The speed sensor measures the rotation of a toothed wheel on a shaft inside the transmission to determine how fast your car is going.
How often should you replace a vehicle or transmission speed sensor?
The average life span of a transmission speed sensor is between 30,000 and 50,000 miles. However, you should change your speed sensor when it starts malfunctioning. Have a qualified mechanic replace your old speed sensor when you notice two or more signs of damage.
How much does it cost to replace a transmission speed sensor?
Engine and transmission speed sensors vary in cost depending on the type of sensor. For example, a crankshaft or camshaft position sensor could cost $15 to $250. Aftermarket parts tend to be cheaper.
Labor varies depending on the engine type, as some sensors are more accessible than others. If your mechanic needs to drop the transmission to replace a transmission sensor, set a budget of $800-1,000.