How Do You Know If Your Speed Sensor Is Bad

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Annually, police pull over about 20 million drivers. A majority of these traffic stops involve incorrect speed. Whether you drive under or over the speed limit, an officer can still stop you and give you a ticket. These tickets come with large fines, court dates, defensive driving courses, and even suspended licenses. In the worst-case scenario, you can even get arrested, especially if you do not pay a fine or attack an officer.

Were you ever pulled over with the premise of speeding, but your speedometer says the correct speed? You may see that the speed is correct, but when measured, it is inaccurate. So why would this happen? An incorrect reading happens most of the time when the vehicle has a faulty speed sensor.

In this guide, we go over how you can know if your speed sensor is faulty through six symptoms of a bad speedometer and the two ways to check a transmission.

To help you understand how to know if you have a bad speed sensor, we wanted to keep things organized and easy for you to find. Under each section, you will get a further explanation on how to determine a faulty speed sensor and how to fix it.

6 Symptoms of a Bad Speed Sensor

A faulty speed sensor reading is common. Many technicians come across speed sensor issues. In fact, there are six different ways the wrong speed may show up. Check out below to see all six.

1. Malfunctioning Cruise Control

The speed sensor not only helps with the speed of your car, but it also regulates the flow of the fuel, ignition timing, and operating the cruise control. The moment your speedometer goes out, it can affect your cruise control. Malfunctioning cruise control can not only annoy you but also cause your vehicle to slow down rapidly. A car rapidly slowing down can cause traffic accidents.

2. Check Engine Light

Another warning sign that you may have a bad speed sensor is if the check engine light appears. Most modern cars have technology features that if any go out, it automatically causes the car to display a check engine light. Anytime you see this light no matter what the issue is, you need to resolve the issues. If you have experience with cars, you can check it out yourself. If not, schedule an appointment with an automotive technician.

3. Long Shifting Intervals

Shifting is the time interval between the gear changing in the transmission. The interval is the time it takes for engine speed to reduce or speed up for the next selected gear. A long shift is anything over 625ms. For most drivers, this does not mean anything. Therefore, if you notice your shifting is not normal, visit an auto shop right away.

Also Read: How to Fix Low Engine Compression?

4. Difficulty Shifting

Manual shifting occurs in cars with stick shifts. Not everyone can drive with a stick shift, especially since most people only drive with one gear, not three. However, if you are a pro at driving a stick shift, you will understand how it feels when things move swiftly and when it does not. You may feel jerks, or you may not be able to move the gear at all. If you have difficulty shifting, then the speed sensor on your transmission is acting up.

5. Overdrive Blinking Issues

Have you ever noticed your car overdrive lights go on and off for no apparent reason? If so, you may have issues with the speed sensor. Unlike many other features on your vehicle, you can push a button and magically resolve the problem. However, you cannot do that with the overdrive lights because they are part of the transmission.

Once the overdrive lights start to flash, your car will store the occurrence or ‘trouble code’ that identifies the type of malfunction. Many people wonder ‘can I drive with a blinking overdrive?’ And the answer is maybe. Anytime you have transmission problems, you should get it evaluated immediately, or your car may break down in the middle of driving.

6. Faulty Speedometer

The last sign of a bad speed sensor is if it is faulty. A faulty speedometer is where the device behaves erratically or does not work at all. Erratic behavior includes the speedometer jumping from one number to the next quickly. For example, the number can start at 55 and randomly jump to 85 in a matter of seconds. If this happens, it most likely means that the cable incurred damages or the sensors on the driveshaft are not accurately sending the signal.

2 Ways to Check a Transmission Speed Sensor

1. Is the Speed Sensor Receiving an Input from the On-Board Computer?

If you think that your speed sensor is incorrect, the first step you must take is to check it out. You can either check it out yourself or visit an automotive technician to help you figure everything out. Here are the two ways to check a transmission on a speed sensor.

Is the Speed Sensor receiving an Input from the On-Board Computer?

Also Read: How To Reset Your Car Computer Without Disconnecting the Battery?

Sometimes technology has a mind of its own. In modern vehicles, technology plays a huge role in how everything functions. If one feature glitches, it can cause issues for the other technical aspects of the vehicle, including the speed sensor.

To check the input, raise the front of the vehicle. Then place it securely on jack stands. Stabilize the wheel to make sure it does not move while you are working on the car. Once everything is stable, find the speed sensor, which is normally attached to the rear of the transmission.

From there, you will follow the wire from the sensor and disconnect it from the wiring harness, which attaches to the car’s frame. Turn on the ignition (but not the engine) and push the probes of a voltmeter into the reference wires in the connectors.

A working speed sensor will have a voltage recorded and displays the speed. A bad speed sensor will not show this information and needs a technician to check it immediately.

2. Is the Speed Sensor defective?

You have looked up and down and all over on your speed sensor. Everything is in its place, and all features are working properly. However, for some reason, the wrong speed is still displaying. If this is the case on your vehicle, then your speed sensor is defective. Anytime you have a defective speed sensor, you need to contact a repair company right away.

You do not necessarily have to go through a mechanic to check to see if your speed sensor is defective. The first thing you should do is reconnect the harness and turn off the ignition. You will remove the electrical connector from the speedometer. After, you will remove the bolt that secures the sensor and transmission. Make sure to remove it gently. You do not want to damage these pieces of equipment.

Then, place the sensor on a bench and check the pulsing AC voltage with the voltmeter as you slowly turn the gear by hand. Once you finish, install the new sensor (if needed) and replace the retaining bolt. Connect the electrical terminal and then test. While working with any wires, be careful and wear the right protective gear. To see if the speed sensor works, your check engine light will disappear. If it does not disappear, visit an automobile mechanic.

Many auto repair shops can alleviate this problem. If you have car insurance, you may even get some of the costs decreased or covered. You can also take your vehicle to the workshop at the auto shop at the dealership you purchased your car from. In most cases, the auto shop can repair the defective speed sensor, whether that be rewiring the technical features or replacing the speed sensor. If they have to replace the entire

speedometer, then your car will stay with the mechanic for a couple of days to a week. Remember to get a rental car so you can get around while waiting for your vehicle.

Depending on the type of vehicle you have and the mechanic you visit, it can range from $160 to $500. We recommend shopping around for the best quote before settling for a mechanic. If the mechanic cannot repair or replace the speed sensor, you may have to adapt to your new inaccurate speed or buy a new motor vehicle.

Common DTCs to expect from a problem with a speed sensor include the following:


Having the wrong speed can get you in loads of trouble with the law and can even cause unwanted accidents. While looking to see if your speedometer is working correctly, make sure to check out these six symptoms as well as the two different ways you can try to resolve the problem. If you do not know how to alleviate the issues, contact your local mechanic today. For more lifestyle information, check out our blog or contact us today.

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