Why is my speedometer going up and down?

Asked By: Javiera Stokoe | Last Updated: 3rd January, 2020
Category: automotive auto safety technologies
4.4/5 (1,658 Views . 27 Votes)
Typically, these malfunctions are caused by, a broken gear in the speedometer system, a speed sensor issue or a faulty engine control unit (ECU). A malfunctioning speedometer may also be due to damaged wiring. In older cars a break in the cable that connects the transmission to the speedometer is the most common cause.

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Simply so, why is my speedometer fluctuating?

If the hairspring comes loose or breaks, it can't hold the speed cup in place, and the result is a fluctuation in the dial. If a speed sensor in the automatic transmission starts to malfunction, it can affect the speedometer and cause fluctuations.

Secondly, what causes the speedometer and odometer to stop working? The most common causes of a speedometer that stopped working include are a faulty speed sensor, a broken gear on the speedometer, damaged wiring, or a faulty engine control unit. DID YOU KNOW: Sometimes you might have an issue where the speedometer is working, but odometer is not.

Correspondingly, what controls speedometer?

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.

How do I know if my speed sensor is bad?

Most Common Symptoms of a Faulty Engine Speed Sensor

  1. Transmission revs higher before it changes gears.
  2. The car's transmission engages into overdrive late and sometimes will never go into that top gear.
  3. Brakes are sometimes harder than normal when coasting.
  4. Speedometer behaves erratically or sometimes does not work at all.

19 Related Question Answers Found

Is the speedometer connected to the transmission?

The speedometer tells you how fast your vehicle is traveling for the purpose of obeying speed laws. Most vehicles use a manual cable hooked to the transmission case to decipher the rpm (revolutions per minute) signal. The speedometer cable, although simple in design, breaks down like any other component.

Can you drive with a broken speed sensor?

That is why in general, it is unsafe to drive a vehicle with a broken wheel speed sensor. If the wheel speed sensor becomes damaged or wears out, initially you probably won't notice much difference in the way your car performs if your ABS light comes on unless you are driving on slippery pavement.

What causes speedometer needle to bounce?

Dirty gunky grease on your cable is the cause. At lower speeds the cable binds slightly and then jumps when the binding is overcome. This causes the spedo needle to jump.

How do you test a transmission speed sensor?

Determine Whether the Speed Sensor is Defective
  1. Reconnect the harness and turn the ignition off.
  2. Place the sensor on a bench and check the pulsing AC voltage with the voltmeter as you slowly turn the gear by hand.
  3. Install the new sensor into the transmission and replace the retaining bolt.

Where is the speed sensor located?


The Vehicle Speed Sensor (VSS) is located on the right rear of the transmission near the tail shaft.

How do I get my speedometer calibrated?

Electronic Speedometer
  1. Determine the distance of the test drive needed to recalibrate your speedometer.
  2. Press and hold the calibration button on the speedometer, start the vehicle and release the button.
  3. Press the button again and drive the distance prescribed by the speedometer manufacturer.

How do you test a car's speedometer?

Divide the number of seconds it took to drive the mile into 3,600, the number of seconds in an hour. This number is your actual mile per hour. Compare your actual mile per hour number to the speed your speedometer indicated. If the indicated speed is higher than the actual speed, the speedometer is fast.

What is wrong when your speedometer stops working?

There are several common causes for a speedometer to stop working. Typically, these malfunctions are caused by, a broken gear in the speedometer system, a speed sensor issue or a faulty engine control unit (ECU). A malfunctioning speedometer may also be due to damaged wiring.

How much is it to replace a speedometer?

Depending on the vehicle year, make and model, a speed sensor can cost as little as $7.92 or as much as $100. For most vehicles, the cost for a speed sensor is between $25 and $45.

Does speed sensor affect odometer?


Primarily, the wheel speed sensors from the ABS system are used along with a vehicle speed sensor. Some cars also have a transmission output shaft speed sensor. This is important because the error that causes the speedometer not to work may not affect the mileage. In my experience, it usually does not.

Can ABS sensor cause transmission problems?

Yes, ABS does affect the transmission. Namely, the vehicle speed sensor is part of the ABS system. This is where your truck reads road speed. The transmission tuning is also based on road speed, and controls when the truck upshifts, downshifts, and when to lock the torque converter.

How does a speed sensor work?

The output shaft speed sensor detects the speed of the drive wheels and sends this information back to the engine control unit. Together these two shafts allow the wheels to rotate at a speed that is manageable while the engine continues to run at a speed that makes it perform efficiently.