Speedometer Not Working - Potential Causes and How to Fix Them

October 27, 2017

A broken speedometer can be an unsettling condition. Though your car may still function, it will make it difficult to know exactly how fast you're driving. As a result you're putting yourself at risk of a traffic ticket at best. At worst you could find yourself driving at a speed that's unsafe for the road conditions.



Common reasons for a broken speedometer

There are many possible reasons behind a faulty speedometer. The most common involve the vehicle speed sensor or an electrical issue. Both problems can have impact in areas of your vehicle outside the speedometer. Knowing what to look for can help you pinpoint what exactly may be cause of a malfunctioning speedometer.

Get it diagnosed by a professional

Bad vehicle speed sensor

Vehicle speed sensors feed information to a number of systems in the car about how fast your vehicle is traveling. The anti-lock brake system (ABS), the speedometer gauge, and cruise control are just a few of the important features of a car that rely on this vehicle speed data to do their jobs.

wheel speed sensor

Wheel speed sensor

Vehicle speed sensors don't fail often, but they are sometimes susceptible to brake dust or damage from road debris. They can also be damaged accidentally during repair work for other reasons involving the wheels, such as brake pad replacement.

If these sensors stop reporting correct data, or fail entirely, the systems they feed can develop problems themselves. In the case of your speedometer, it may read incorrect speeds or not register any speed at all. If the wheel speed sensor is the cause of a speedometer failure, the ABS and check engine lights will typically turn on as well.

Solution: If a bad sensor turns out to be the primary cause, the solution will most likely be to replace the wheel speed sensor.

Electrical or computer problems

Behind the scenes of your speedometer, there's a computer and electrical system that helps relay signals about how fast your car is moving, among many other things. This computer is known as the engine control module (ECM). If the ECM fails to do its job properly, it can manifest itself in a number of ways. One of those ways is the speedometer may no longer report the correct speed of your vehicle.

The causes of an electrical failure could range from a short-circuit, to a blown fuse, to a physically damaged control module. The only way to know for sure if this is the cause of a speedometer failure is to have a trained technician test and diagnose the entire system.

Solution: If it's been determined that an electrical problem is at the root of a wonky speedometer, the solution will depend on the exact point of failure. Some cases could simply involve fixing a bad wire, or it could require replacing the entire engine control module. For an accurate identification of the issue we recommend having an experienced, trained technician diagnose the electrical issue.

More information on speedometer problems

About the Author

John Gower is an automotive expert at RepairPal, the leading online source of auto repair resources and estimates. With many ASE Master certified mechanics on staff who have decades of experience, RepairPal knows all the fine points of car repair.

2 User Comments

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By , May 02, 2018
The air bag light is on, the engine light and the speedometer computer system is not recording the correct speed
By , December 12, 2018
Yes on my 95 blazer my speedometer quit my cruise, ac, all in one day it also quit shifting I've changed the vss I've put a new ecm in a new vssb and none of this has made a difference what else could it be