How Long Can You Drive a Car With a Bad Speed Sensor?

A car’s speed sensor is responsible for sending and receiving signals, which then in return sends speed and rpm information to the computer. Speed sensors malfunction in different ways. It can be that the signal it sends has a glitch or that it stops working altogether. Other times, you may experience ‘check engine lights due to issues with the signal the sensor sends. If you do run into such issues with your car, there are faster approaches for getting it fixed than changing the spare part altogether.

Now the big question is, how long can you drive your car with a bad speed sensor?

Usually, a speed sensor irregularity will not cause your car to stop running, so you might still be able to drive over long distances. However, modern cars have gotten really smart, and with the integration of systems, a faulty speed wheel could bring your vehicle to a halt.

What are speed sensors?

 It’s vital to understand the role of a speed sensor before thinking about how long you can drive without one or all.

Speed sensors are attached to each wheel in a car, meaning that if your vehicle has four wheels, it also has four speed sensors. These speed sensors’ sole function is to detect the wheel’s speed and send the information in the form of electric signals to the transmission/ESP/ABS control unit system. Notably, the speed sensors on modern cars can detect the rotational speed of the wheel they are attached to.

What happens when speed sensors break?

With that in mind, here’s what happens when one of them is not working correctly:

When a speed sensor is faulty or completely broken, it could send wrong or no signals at all to the connected system. This can be the ESP, ABS, or ECM system.

When the ABS interpret these wrong signals, it could lead to anomalies like difficulty in changing gears, or some driver assistant functions like cruise control might begin to malfunction.

Therefore, while a bad speed sensor does not stop your car from running, it sends bad signals to the ABS or transmission, which in turn interferes with how some of the smart features operate.

That said, it’s dangerous and not advisable to drive a car with bad speed sensors. More so because they are fast and cheap to replace. Consequently, even when it’s just one of them that’s malfunctioning, it’s always advisable to change all of them.

Signs that your car has a bad speed sensor            

Here are a few indicators that one or several of your car’s speed sensors is not functioning properly:

1. Transmission problems

As we’ve seen, one of the results of a bad speed sensor is having difficulty changing gears. This is because the vehicle speed information relayed to the transmission from the speed sensors determines shift timing in automatic cars. As a result, one of the most recurrent signs of a bad speed sensor is hard shifts, delayed shifts, and limited gear operation.

2. Inability to engage cruise control

Normally, your vehicle’s cruise control will be disabled automatically by the  PCM when it fails to receive information from the VSS. This is because cruise controls require the speed data to keep your vehicle running at a constant speed.

3. Irregular speedometer readings

Most vehicles use the VSS as the main input for speedometer readings. Consequently, any issues with the speed sensors will cause erratic or no speedometer readings at all.

Your vehicle will continue to run with or without speedometer readings. However, driving without knowing how fast you’re going is quite dangerous.

4. Check engine light is triggered.

The PCM can trigger your check engine light for various reasons. One of these reasons is a faulty VSS. To confirm if a VSS malfunction has triggered the light, you’ll need to connect your vehicle to an OBD-II scan tool.

5. Lack of torque converter clutch application

The torque converter clutch is activated at a pre-programmed speed. Without correct speed information from the VSS, the torque converter will not be able to apply the clutch and form a mechanical link between the transmission and the engine.

What causes speed sensors to fail?

Now that you know what happens when speed sensors fail, let’s look at what causes them to fail in the first place:

Damage to the sensor itself

The most obvious cause for a speed sensor failure is physical damage to the speed sensor itself. It is possible for the speed sensor to get cracked. The plastic portion can also become brittle after prolonged use. Additionally, the magnetic part of the sensor is vulnerable to wear and tear after extended use.

An electrical problem in the sensor

Since the speed sensor communicates through electrical signals, an internal electrical fault can result in a bad signal or no signal at all. To ascertain this, you can test the speed sensor with an oscilloscope or a voltmeter.

Poor vehicle maintenance

Failing to adhere to your vehicle maintenance schedule can increase the risk of some speed sensors malfunctioning. This is because they cannot give accurate readings when the magnetic pickup or toothed wheel are heavily covered in gunk, especially old transmission fluid contaminants.        

How do you know which ABS sensor has failed?

Dismantling your wheel hub and checking if the ABS sensor is damaged is not a guaranteed way of telling if it’s working properly. While this might work if the sensor is physically damaged, there are no visual signs of malfunction if the sensor has internal problems.

As a result, you will need a troubleshooting device to run diagnostic tests and pinpoint exactly which sensors are problematic.                                                                                                                                                                                                           How long can you drive a car with bad Transmission sensors?

Don’t get confused here. Wheel sensors are also called transmission sensors for the reasons we saw above. In fact, they are also called ABS sensors and wheel speed sensors.

To wrap it up

Speed sensors are a small but vital component in any modern car. Always contact your repair shop whenever you suspect that they are not working properly.