What happens when speedometer cable goes out?

According to the US Department of Transportation, there were 42 million speeding tickets issued to United States licensed drivers in 2014. Although many of these drivers might claim their speedometer was broken when fighting the ticket, they'd be surprised to learn that this defense would result in another citation for a broken speedometer. A speedometer on any vehicle is an important safety device that is susceptible to breaking or falling out of calibration. The culprit of most speedometer issues is the speedometer cable or housing.

How a speedometer works

Prior to the early 1980's, the speedometers used in vehicles were mechanical in nature. The patent of the Otto Schulze-designed speedometer dates back to 1902, and was the primary speedometer used in vehicles across the globe for more than 80 years. Although they were very precise mechanical devices, they were very susceptible to falling out of calibration, or breaking entirely. This gave way to the electronic speedometer used in our cars today.

With an electric speedometer, the speedometer cable is attached to a drive gear inside the transmission or driveshaft and measures rotation through electrical pulses, then translates the duration of the electrical signal into the speed as you are driving. A secondary speedometer cable is attached to a wheel sensor and measures distance; which powers the odometer. The speedometer cable sends all of this information to the instrument panel where it is relayed to the speedometer.

The cable housing is a protective sheath that surrounds the cable to prevent it from being damaged. These two components work in conjunction to power the speedometer and deliver an accurate reading. Over time, they can fail due to damage, or wear and tear. Here are a few of the warning signs to consider that may be a strong indicator of speedometer cable or housing that may be failing:

Speedometer speed fluctuates erratically

Regardless of whether you have a manual gauge or an LED powered digital speedometer, they both share one similarity – smooth transition. When you accelerate or decelerate, your speedometer displays the speed progressively, meaning that it doesn't just jump from 45 to 55 mph instantly; it's a progressive climb from 45, 46, and 47 and so on. While you are driving, if you notice the needle on the speedometer jumps erratically from one number to another, the speedometer cable is most likely damaged or the sensors on the driveshaft are not accurately sending the signal through the cable.

Sometimes this problem can be solved by having a mechanic lubricate the cable housing or clean the sensors, as long as there is no damage to the sensors or cable. In some cases, the housing or cable is cut or has frays that are causing the erratic behavior of the speedometer. If this occurs, the entire cable and housing needs to be replaced.

Speedometer does not register

Another warning sign of a problem with the speedometer cable or housing is when the speedometer doesn't register any speed at all. If the needle on your speedometer does not move or the LED lights do not register a speed on the dash, it's likely that the speedometer cable and housing have already failed. However, this problem might also be caused by a faulty fuse or electrical connection to the dashboard. In either case, a certified mechanic should be contacted immediately to inspect, diagnose and repair the problem.

Squealing noises coming from the dashboard or below the car

When a speedometer cable and housing are failing, they may make squealing noises. The noise is also associated with the speedometer needle jumping around erratically as we explained above. The noises typically come from the dashboard of your vehicle, specifically where the speedometer is located. However, they might also come from the other source of attachment, the transmission under your car. As soon as you notice these noises, contact YourMechanic to have the speedometer cable and housing looked at immediately. If caught early it is possible for the mechanic to clean or repair the issue before it fails.

The speedometer itself does not typically break as it's designed to simply display information that it is sent through the cable. Both the cable and housing are exposed underneath your car, to different road conditions, weather, debris and other items that cause the speedometer cable and housing to fail. If you notice any of the warning signs noted above, don't delay. Contact YourMechanic today to schedule an appointment to stay safe and reduce the potential of getting a speeding ticket.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Last Updated on December 13, 2021

We seldom give even a passing thought to the operation of our vehicle’s speedometer, until a malfunction of one type or another has rendered it inoperable. Without a fully functioning speedometer, one is left with little recourse when attempting to travel at the appropriate speed. This, in itself, can be quite concerning.

While many crafty DIY mechanics are more than capable of handling a tune-up, or completing a brake job, far fewer know where to begin, when faced with a broken speedometer. Though some issues of this type do tend to be rather complex in nature, others are far less troubling and can be repaired in a prompt manner.

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The following guide will assist you in understanding the principles of speedometer operation, and point you in the right direction, should your vehicle’s speedometer exhibit troubling symptoms.

• How a Speedometer Works
  • Cable-Driven Speedometer
  • Electronic Speedometer
• Reasons Your Speedometer Doesn’t Work
• How to Fix a Broken Speedometer
• Can You Still Drive Your Car If the Speedometer Doesn’t Work?
• Can You Use Your Phone as a Speedometer Instead?
• How Much Does it Cost to Fix a Speedometer?

How a Speedometer Works

Quite simply, a speedometer is a device that measures the speed of a vehicle’s travel, to a high degree of accuracy. For decades, vehicles of every type have come standard with an in-dash speedometer.

Cable-Driven Speedometer

The vast majority of early speedometers were of a cable design. Most of these systems utilized a flexible cable, which was affixed to a gear, driven by the transmission’s output shaft. At the opposing end of the speedometer cable, was a magnet, which spun within a speed cup. 

The resulting magnetic field placed the speed cup, itself, into motion. The rotation of this speed cup sweeps the attached gauged needle, thereby providing motorists with an accurate reading of their vehicle’s speed.

Electronic Speedometer

Modern vehicles now rely upon the use of electronic speedometers. These speedometers utilize a speed sensor that detects pulses from the teeth of a gear, mounted on the output side of a vehicle’s transmission.

These pulses are interpreted by a vehicle’s control module, which then sends a correlated signal to the vehicle’s instrument cluster.

The pulse rate detected by a vehicle’s speed sensor increases upon acceleration, thereby varying the signal presented to the corresponding module. Likewise, deceleration causes an opposite reaction, in regards to speed sensor pulse rate.

Reasons Your Speedometer Doesn’t Work

There are several reasons that a vehicle’s speedometer can fail. However, some failures are far more probable than others. The following are a number of the most common root causes of speedometer related issues.

• Damaged or faulty speed sensor
• Damaged speed sensor wiring
• Compromised instrument cluster
• Failed ECU

How to Fix a Broken Speedometer

Before speedometer repair can take place, one must first determine the root cause of their vehicle’s issue. Speed sensor function and circuit integrity can be validated through the use of a multimeter, or high-end scan tool. Likewise, a vehicle’s instrument cluster can be checked with the use of a bi-directional scan tool.

Related: Code P0500 (Speed Sensor Malfunction)

A simple visual inspection can also pay dividends when attempting to diagnose a speedometer related issue. A vehicle’s speed sensor, as well as its corresponding wiring and connectors, should be checked for signs of damage or degradation. One can also observe instrument cluster function, in a search for irregularities. In many cases, one will note that the speedometer needle is jumping, or that a failure occurs in an intermittent fashion.

If you have determined that your vehicle’s speed sensor is defective, a replacement will be necessary. This simply involves removing the affected sensor’s hold-down fastener, pulling the sensor from its bore, and replacing the sensor in question. 

Wiring faults are somewhat more difficult to repair and involve locating the damaged segment of the affected circuit. In such a case, a replacement harness or pigtail can be purchased. Alternatively, in certain cases, circuit repair might be possible.

If your vehicle’s speedometer is found to be defective, instrument cluster removal will be necessary. This often involves the removal of select dash components, and associated hardware. One can then purchase a new/remanufactured instrument cluster, or choose to have their compromised cluster rebuilt.

In the event that ECU failure is suspected, further diagnostics should be conducted in accordance with factory-specific service literature. Though computers of this type do indeed fail on occasion, issues of this nature are relatively rare.

Can You Still Drive Your Car If the Speedometer Doesn’t Work?

Technically speaking, it is possible to drive a vehicle with an inoperable speedometer. However, doing so is not recommended.

Without an alternative solution at the ready, you will be unable to recognize the speed at which your vehicle is traveling. This is not only dangerous but significantly increases the risk of being cited by law enforcement for a moving violation.

Simply put, you are highly unlikely to get out of a speeding ticket just because your speedometer is not working. In any event, a malfunctioning speedometer should be addressed at the first available opportunity.

Can You Use Your Phone as a Speedometer Instead?

All modern smartphones are GPS enabled. As a result, your phone is able to accurately chart its own location, as well as its speed of travel. A number of inquisitive individuals have seized upon this knowledge, by developing speed-tracking apps.

In the event of speedometer failure, a speed-tracking app such as the popular apps Speedometer Speed Box (for iPhone) or GPS Speedometer (for Android) can be used to keep tabs on your vehicle’s speed. Many other similar apps (free and paid) exist that accomplish the same purpose.

However, motorists should be cautioned that apps of this nature are not always completely accurate. Therefore, it is best to only use such apps as a fall-back option, until your vehicle’s speedometer issues can be resolved.

How Much Does it Cost to Fix a Speedometer?

The cost of fixing a vehicle’s speedometer is highly variable and is largely dependent upon the root cause of the failure at hand. This cost also varies, between that associated with DIY repair, and repair at a shop or other repair facility.

The most common speedometer related issue is that which pertains to speed sensor failure. Most shops charge between $100-$250 for in-house speed sensor replacement. However, DIY costs tend to be significantly less, as only the cost of the sensor itself will be absorbed. In many cases, a sensor of this nature can be purchased for as little as $25-$40.

If the issue at hand pertains to an instrument cluster failure, the cost of repair can be significantly higher. Even a rebuilt instrument cluster can be quite pricey, often ranging from $200-$400 in total cost.

The price of a new speedometer/instrument cluster tends to be considerably higher. It might also be necessary to have a dealership program your vehicle’s new instrument cluster, for an additional fee.

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