how to fix a speedometer

By Tsukasa Azuma

Last updated Feb 18, 2019

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How do you know about the speed you are driving at? Well, the speedometer is the instrument to look at when you want to know the instant speed readings. Safety on the road depends on many factors and maintaining the right speed limit is one of them. So, when the car speedometer not working , you don't know whether you are driving too slow or fast. This could be dangerous on a road where driving at a low speed is essential for safe driving. Also, you can get booked by a police officer for breaking the maximum speed limit.

Know the symptoms and reasons for a defective speedometer. Also, some suggestions and advice would be helpful in deciding how to fix it.

Symptoms of Car Speedometer Not Working

The speedometer determines the vehicle's speed by drawing information from the transmission and driveshaft. The ECU (engine control unit) converts the driveshaft's rotation speed to the vehicle's linear speed and then passes the information to the speedometer. When the car speedometer not working, it cannot translate that information coming from the ECU.

A failed speedometer poses a potential safety threat. The warning signs to look for are:

The speedometer is completely dead ! An issue with the speed sensors or speedometer head is the reason. Worn out connecting cables are the culprits in older cars.

Check engine light comes on . It happens due to a faulty sensor that cannot process the information received from the ECU. It also causes the speedometer behaving erratically.

what causes the speedometer to stop working — The check engine light may come on as a symptom

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Frequent changes in the readings . The problem also occurs due to bad wiring or faulty sensors. Re-calibrating the sensors or repairing the wires will solve the issue.

Faulty readings. Changing the tires that are larger than the manufacturer's recommended dimensions are the culprit in this case. The speedometer shows wrong readings because it is calibrated to the dimensions of the factory-fitted tires.

What Causes The Speedometer To Stop Working?

The speedometers in modern vehicles use speed sensors to calculate the speed while the older models make use of gears and wires for the same purpose. The speedometer stops functioning when the sensors don't work, dials malfunction, or the wiring becomes bad.

Look into these components when the car speedometer not working .

Malfunctioning Speed Sensor

A speed sensor does not only indicate the vehicle speed but also help with cruise control operation and regulation of the fuel's flowing and ignition timing. A speedometer may stop working due to a bad sensor. Plus, the affected cruise control can disrupt the driving functions of the car. Any problem with the sensor will make the Check Engine light to come on.

Issues with the ECU

The Engine Control Unit (ECU) is literally the hub of engine activities – acting as the car's computer brain. It monitors and controls multiple engine activities, including speed. It's obvious that the speedometer may give wrong readings in case of certain ECU problems.

Defective Wiring and/or Fuse

Another reason for the car speedometer not working is a bad wire. The wires can short out for many reasons, causing the fuse to blow out and stopping the operation of the speedometer. It mainly happens in older cars.

My Speedometer Stopped Working: How Do I Fix It?

Depending on the type, there is only one repair solution for a bad speedometer – replacing either the speed sensor or the wiring. With proper knowledge about the mechanism of a motor vehicle, you can carry out the repair job at your garage. Otherwise, taking professional help is the most logical thing to do.

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Using a code scanner to examine the error codes is the first step to reach the root of the trouble. Connecting the scanner to the ECU will help to pinpoint the failed components. It is necessary to clear the error code to complete the repair process.

1. When The Sensors Have Failed…

Find the location of the sensors and check them along with the wires connecting to them for any visible damage. Replace the older one with the new unit in case if you have found any defect.

2. When The Wiring Is Bad…

The wires can short or worn out in an older car and cause the fuse to blow out. Examine both wiring and the fuse and replace the faulty ones.

3. If The ECU Is The Culprit Here…

The entire ECU needs replacement. You can reset it but it will only be a temporary fix. Remember to rotate the ignition key to the 'Auxiliary' position after the installation of the new unit. It will help the ECU to kick off the operation and start adjusting to the other engine systems when the car is turned on.

In every case, don't forget to test drive the car to make sure that the speedometer is working properly. These are the repair processes that you should resort to when the car speedometer not working .