Blog Car Care Advice Why Is My Speedometer Not Working? (5 Reasons + Fixes)
Car Care Advice

Why Is My Speedometer Not Working? (5 Reasons + Fixes)

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Cruising down the road without a speedometer is almost like a blind man’s game. 
But not if you can diagnose and fix the defective speedometer before it brings you trouble.

Wondering how you can do that?
Well, you’re in luck!

This article covers five reasons why your speedometer is not working, how to fix it, and its cost. We’ll also cover some interesting FAQs, like if you can use a mobile phone to read speed.

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Let’s get started!

5 Reasons Why Your Speedometer is Not Working

Here are a few reasons for your speedometer not working:

1. Malfunctioning Wheel Speed Sensors

Your speedometer is directly linked to the speed sensor — meaning if anything goes wrong with the vehicle speed sensor, it’ll lead to a speedometer failure.

Whether you have hall effect or digital speed sensors, here are some signs of a bad sensor that may accompany your erratic speedometer needle:

2. Bad Wiring

If your speedometer flickers between two different speeds, a bad wire, wiring harness, or cable may be the culprit. This happens when the speedometer cable wears out, or the fuse blows up.

For example, an exposed wire or electrical connecter can short out in wet environments due to moisture — blowing out the fuse. And if your fuse goes out, your car speedometer can drop to zero. 

3. Faulty Instrument Cluster

The instrument cluster (gauge cluster) on the dashboard is a collection of indicators and gauges that give complete information about your car’s state, like odometer reading, vehicle speed, and more.

A failing instrument cluster is bad news cause the speedo will either stop working or show wrong vehicle speed readings. This can be caused by a damaged instrument panel wiring harness. 

A bad instrument cluster is usually accompanied by other inaccurate readings by the coolant temperature gauge, fuel gauge, or odometer. 

4. Vehicle Alterations

Modifying older cars (or any vehicle, for that matter) can result in a malfunctioning speedometer. For example, replacing your vehicle’s original tire with a taller one may lead to incorrect speedometer readings.

Why’s that?
When your vehicle is new, the speedometer is recalibrated according to the exact size of the tire. When you opt for a bigger tire size, the tire’s circumference will also be greater — meaning a single rotation will cover more distance than your previous smaller tires. 

Unless you get your speedometer recalibrated to the new tires, it’ll show slower speed readings.

5. Malfunctioning ECU

Another reason for your speedometer not working is a faulty Electrical Control Unit (ECU). A modern vehicle comes with an ECU that controls many internal engine systems, from the fuel injector to braking and suspension systems.

If the ECU is acting up, your vehicle may be unable to read the speed signal from the speed sensor. It’ll fail to identify the correct traveling speed — ultimately leading to a fluctuating speedometer needle or even a zero reading.

You can also check if your inaccurate speedometer readings are accompanied by other signs of malfunctioning ECU, like inaccurate fuel gauge readings, misfires, or a lit check engine light.

So how do we fix a speedometer problem?
Let’s find out.

How to Diagnose and Fix Your Speedometer

In cases of major custom vehicle alterations, recalibrating the speedometer may resolve the problem.

If that doesn’t fix your car speedometer, here’s how a mechanic may fix your defective speedometer:

1. Check Error Codes

If your check engine light is on, your mechanic may start the diagnosis by using a code reader to check what error codes show up or if other related warning lights, like the ABS light, show up. Checking these codes may give the mechanic a better picture of the components causing the speedometer failure.

Your mechanic might also check the instrument cluster (gauge cluster) with a bi-directional scan tool to find potential causes.  

2. Failed Speed Sensor

If the mechanic suspects a bad sensor, they may get underneath the car to check the wheel speed sensors and the wiring for any signs of damage or degradation. 

In case they spot a bad speed sensor, the mechanic will replace it with a new one.

Simple: The mechanic may remove the faulty speed sensor’s hold-down fastener, pull the bad sensor from its bore and replace it with a new one. 

3. Bad Wiring

Your mechanic may check for damages in any electrical connector, wire, or speedometer cable connecting the speedometer to the vehicle speed sensor. If needed, your mechanic will replace the necessary cable or wire to fix the broken speedometer.

Additionally, they may replace the fuse if they find a blown fuse.

4. Malfunctioning ECU

If your ECU isn’t working, you’ll probably need to replace it — especially since resetting the ECU is only a temporary fix.

After your mechanic replaces the ECU, they’ll turn the ignition key to the auxiliary position, turning on the ECU. This allows the ECU to optimize internal vehicle systems when you start your vehicle.

After fixing the root causes of the defective speedometer, your mechanic may use the code scanner to check if all trouble codes are cleared. They may also test drive your car to ensure you have a perfectly working speedometer. 

Next, let’s check out how much these fixes cost.

How Much Will it Cost to Fix My Speedometer?

A speedometer repair or replacement costs depend on the vehicle model, spare parts costs, and local labor charges.

You can expect to pay around $100- $250 for a basic speedometer repair and nearly $200 – $400 for a major speedo problem.

If you still have doubts, let these frequently asked questions on speedometers clear them for you.

4 FAQs on Speedometer

Here are the answers to some common speedometer related questions:

1. What is a Speedometer?

A speedometer, located in the dashboard, measures your driving speed. 

In some vehicles, the speedometer is a gauge or needle that climbs upwards as you increase your driving speed. If you drive a modern vehicle, a digitally rendered number may show your speed reading. 

2. How Does a Speedometer Work?

A car speedometer calculates your vehicle speed by detecting the speed at which your wheels rotate. 

The ECU translates the driveshaft’s rotational speed into your vehicle’s linear speed and transmits it to you via the speedometer. 

There are two types of speedometers:

3. Can I Drive Without a Speedometer?

Technically yes.

But it’s not recommended because you won’t know how fast you’re driving with a broken speedometer, whether it’s a mechanical or electronic speedo. Not only is this dangerous, but you can be fined heavily for speed limit violations and driving with a malfunctioning speedometer.

4. Can I Use My Phone as a Replacement Speedometer?

Since most modern mobile phones are GPS enabled, they can track your location and calculate your travel speed. There are also speedometer and odometer apps that help track your vehicle’s speed and distance covered.

However, it may not be as accurate as your working speedometer, and before you know it, you may be fined for driving over the vehicle speed limit. 

Using a phone as a speedometer is also illegal in many countries. So ensure you check your local laws before driving without a speedo. 

Wrapping Up

Diagnosing a malfunctioning speedometer on your own can be a challenging feat as it’s caused by a range of issues, from a blown fuse and bad wire to a bad speed sensor. 

That’s why you need the help of experts like AutoNation Mobile Service!

AutoNation Mobile Service, a mobile repair service, offers upfront pricing, convenient online booking, and a 12-Month, 12,000-Mile warranty on all repairs — available seven days a week.

So the next time you have a speedometer problem, contact us, and our experts will drop by to fix it for you in no time.