Nowadays, all modern car manufacturers produce vehicles with anti-lock brakes (ABS). Before we start on how to test the wheel speed sensor, let’s see some information about a wheel speed sensor and an anti-lock brake system.
In what way are these two interlinked? It is necessary to have good ABS brakes to achieve the utmost safety for the car and its passengers by reducing the chances of a serious collision on the road.
“ABS wheel speed sensor failure may end in Life failure”
What is an ABS wheel speed sensor?
An ABS wheel speed sensor, also known as a vehicle speed sensor, is a kind of tachometer that is connected to all four wheels and is used to measure the rotational speed of each wheel in terms of revolutions per minute (RPM) through an analog indicator or through a digital indicator.
What is the anti-lock brake system and how does it work in harmony with the wheel speed sensor?
When the vehicle is running, the ABS wheel speed sensor will start sensing the rotational speed of the wheels and keep on sending electromagnetic signals continuously to the anti-lock brake system.
When the vehicle faces a situation where a sudden brake is applied, the brakes might be locked due to which the vehicle may skid or collide.
In order to avoid this locking-up of the brakes, this anti-lock brake system (ABS) has been designed. In this instance, ABS will release pressure and re-pump the brakes when a lockup is detected on that particular wheel or wheels.
This means that when the anti-brake system detects a significant change in the signals sent by the ABS wheel speed sensor, it will activate in a matter of seconds.
This prevents the wheels from skidding, allowing the driver to regain control of the vehicle and avoid any embarrassing incidents. the strategy behind the function of ABS. Now we feel the importance of an anti-lock brake system.
At the same time, we cannot neglect the most vital function that the wheel speed sensor has performed at the time of a heavy braking situation.
Because of the signals received from the wheel speed sensor, the anti-lock brakes can act fast and put things under control.
Reasons for wheel speed sensor failure
An ABS wheel speed sensor becoming a failure is a common problem that is faced by all. This happens because the wheel speed sensor is positioned on the ABS wheel in an unfavorable situation.
They get spoiled often because they are exposed to water, heat, snow, and pollution on and off the road. Sometimes, the wheel speed sensor may get spoiled due to the improper handling of the wire that connects the sensor to the wheel.
In some cases, when other parts like brake pedals or axles are changed, there is a chance that the sensor or the wire connecting it may get damaged.
When there is an issue with the battery, it may result in the speed sensor failing. The sensor is made of magnets. When any metal part comes into contact or is placed wrongly, it may result in malfunctioning.
When it gets covered with some mud or things like that, it results in the ABS light coming on, but the fact is there is no such problem, only the dirt makes it unable to function.
It can be cleaned with water, but if the ABS wheel speed sensor is damaged, it can be easily replaced by a mechanic. It could cost anywhere between $123 and $665.
Even a deflated tire can lead to wheel speed sensor failure. Hence, it is advised to maintain the prescribed air pressure for the wheels.
How can we smell a wheel speed sensor failure?
When the wheel speed sensor does not work, the traction controls light and ABS light will both glow on the dashboard.
Traction control is also measured by the computer through the wheel speed sensor, so when it gets damaged, the traction control lights turn on.
The next outcome may be that the wheels may get locked. The traction control may stop working as the wheel speed sensor does not work.
Sometimes, the car cannot be accelerated. Another thing that one may feel while driving is that the gears may not change smoothly.
There will be a mismatch between the readings shown by the speedometer and the actual speed of the car.
How to test transmission speed sensor?
A transmission speed sensor is an important device in the car that enables the car to coordinate the engine function with the transmission.
The information the computer gets from the transmission speed sensor and from other sensors considered together is used to calibrate the engine, arrange the shift points, and so on.
To test a transmission speed sensor, a Board Diagnostic scanner-2 can be used. This would let us know if there are any code errors with regard to the transmission speed sensor.
If such an error is detected, then the part must be changed. After changing the transmission speed sensor, take a test drive and ensure that the transmission shifts are happening well.
Ensure that the cruise control is functioning well. Generally, when a transmission speed sensor is not working, check engine lights will be on.
When all is reset, ensure that the check engine light is turned off. Removing or changing a transmission speed sensor must be done by a professional as any mistake may cause worse effects, as it is measuring the transmission shaft and the RPM and it contains some electrical parts that should not be damaged.
Driving a car with a defective transmission speed sensor is not advisable as the car’s computer is dependent on the sensor to determine the speed of the car, and hence it may cause the application of brakes to an undesired level.
How to test wheel speed sensor with a multimeter?
The ABS wheel speed sensor reads the rotational speed and sends the pulse to the anti-lock brake system and the driver too.
While driving, it is essential to know at what speed the vehicle is cruising and to have the control that we are not overspeeding the vehicle.
If we think it is malfunctioning, then we should test the wheel speed sensor using a multimeter in the following steps.
- Step 1: First, we need to check the car manual for anti-lock brake resistance. In most cars, it would be 50 ohms. Next, check whether the ABS is connected only to the front wheels or to all four wheels. If it is connected to all four wheels, then you need to check all four wheels because the brake light will not indicate which sensor among the four wheels is causing the problem.
- Step 2: Next, we need to ensure that we have all the below-listed necessary things on hand so that we can avoid any rushing for tools in between tests.
- Car Manual
- Jack for lifting a car.
- A jack stand for your car
- Car tire iron
- An assistant
- A torque wrench
- Step 3: Once we are ready, we shall park the vehicle in a flat, grounded level and turn off the engine. Keep the gear in the neutral position and apply the hand brake or the emergency brake.
- Step 4: Start lifting the car using a lifting jack to remove the tire for testing purposes. Now it will be easy to test the wheel sensor since the car will get into the correct position and we will be able to see if the wheel speed sensor is connected with an electrical connector wire. In most cars, it is located beside the wheel frame. We can disconnect the sensor wire by removing the safety clamp and pulling away the wire.
- Step 5: Now we can see the terminals of the speed sensor. Next, we need to connect the multimeter testing probe with the speed sensor with the help of a connecting clamp that comes with the multimeter.
- Step 6: Now it is very important that while connecting the speed sensor’s terminals for testing the wheel speed sensor with the multimeter testing probe, you ensure that the probes do not touch each other. Failing that, the sensors will give wrong readings. Even when the speed sensor terminals and multimeter probes are not properly connected, it will get only an improperly fluctuated reading.
- Step 7: After ensuring both the sensor terminals and the multimeter probes are connected well, we can now turn on the AC voltage. At once, we can notice a jump in the readings on the multimeter, both up and down. Now the sensor is ready for testing, and we can finally see the test progress.
- Step 8: It is implied that the wheel hub creates voltage and that we can notice the multimeter spin, which is based on the wheel speed. So, in order to get the readings on the multimeter, we need to spin the wheel hub. Now we can notice that the reading varies depending upon the speed of the spinning wheel hub. Once the wheel hub is stopped, the reading on the multimeter comes down to zero. The reading should be very close to the car manual value and the variation should be less than 10% of the prescribed value.
- Step 9: If we see that the reading goes up when we are spinning the wheel hub and there is zero reading when spinning is stopped, we come to the conclusion that the sensor is working properly. In the same way, we can start checking the next wheel speed sensor one after another. If there is no reading even though the wheel hub is spinning, it shows that the wheel speed sensor for the wheel is causing the problem. Before we decide on a wheel speed sensor replacement for that wheel, we need to do a check for continuity function. By this way, we can check the passing of an electrical impulse from end to end. If there is a short or burnt wire, there will be a lack of continuity, and this testing allows us to find the damaged portion of the wire that is preventing continuity and fix it accordingly. Otherwise, you’ll need to replace the speed sensor.
- Step 10: Once we find out which wheel speed sensor is malfunctioning, unscrew any nuts or clamps holding the sensor and remove it from the vehicle. Once you have detached the sensor, gently clean the area with a cleaning fluid and a cloth. Also check for any rust formation. If so, use sandpaper to scratch the rusted surface. Now the new wheel speed sensor can be fitted and tightened with the screws or clamps holding the sensor. Now again, test the new sensor with the multimeter as earlier, but this time it will show the reading when the wheel hub spins. If any brake shoes or rotors have been removed in order to have a clear view during the process of testing, put them back in their place.
Thus, the process of testing wheel speed sensor using a multimeter is done.
Once all the parts are assembled correctly back into their positions and you’re done with all the brake shoes and parts of the speed sensors, it’s time to fit the wheels back onto the hub and tighten the nuts by hand initially.
Now get the jack lower and the car will come back to its default stature on the ground. Then, using a torque wrench, tighten the nuts firmly according to the capacity of the vehicle. The torque range applicable to your car can be checked with the car’s user manual.
The irony here is that even a powerful anti-lock brake system without any issues and capable of stabilizing the wheels and preventing them from locking up, allowing the driver to move the stirrings easily in a matter of seconds, may become useless and prone to accidents.
This is a worse thing that can happen if there is no signal from the ABS wheel speed sensor. The ABS will not work as if there was no heavy braking situation.
“A single stitch at the right time saves nine”. Thus, by knowing how to test wheel speed sensor can prevent many unpleasant journey experiences.