/ / / Peterbilt Speedometer Not Working: 5 Malfunctioning Causes Listed!

Peterbilt Speedometer Not Working: 5 Malfunctioning Causes Listed!

Peterbilt speedometer not working makes monitoring the vehicle’s speed difficult and can lead to potential safety issues. Troubleshooting the speedometer problem is done by a mechanic or by following some DIY steps.

In this article, we’ll explore the five causes of Peterbilt truck speedometer issues and how to diagnose and fix them like a pro. Let’s begin!

Reasons Why Peterbilt Speedometer Not Working

The Peterbilt 379 is a popular truck. It is well-known for its sturdiness and boasts several strong features. Yet it also develops issues over time, like every piece of equipment.

Reasons for Peterbilt Speedometer Malfunction

According to numerous users, the speedometer in the Peterbilt truck occasionally can stop working. If this happens, it could be due to various reasons, including:

  • A faulty speed sensor
  • Wiring damage
  • Defective speedometer head
  • A blown fuse
  • A broken stepper motor

The reasons for Peterbilt speedometer trouble vary. By understanding them, you can begin to troubleshoot the issue and find a solution that works for you.

Identifying and Resolving Speedometer Issues in Peterbilt 379

Peterbilt 379 truck can face various speedometer issues, as outlined earlier. In this section, we will discuss them in detail and provide solutions.

Speedometer Peterbilt 379

1. Defective Wiring

If the speedometer stops working properly, check its wiring harness first. This can happen due to the following;

  • Worn-out or broken wiring harness
  • A bad connection
  • Short circuit
  • If the wires are burnt, damaged, or open at the ends

Additionally, check the condition of the instrument cluster on your Peterbilt 379 truck. Voltmeter verifies the dependability of the instrument cluster.

Important: It is essential to remember that the board’s other gauges will stop functioning if the instrument cluster is damaged. Instrument cluster lines transfer current to different locations. If they are damaged, they won’t be able to carry the current. This will cause your Peterbilt 379 truck’s speedometer to cease working properly.


There are things you need to do:

  • Replacing wires brings the faulty speedometer of the Peterbilt 379 truck to life.
  • Change or repair any broken wires or corroded connections.
  • Ensure that the connectors are plugged in securely.

Attention! Do not handle the wires without the necessary tools and knowledge. Consider contacting a qualified mechanic who will fix everything.

If you’re unfamiliar with how to check the wiring, this video provides step-by-step instructions on diagnosing and repairing wiring issues related to the speedometer. Carrying out the checks correctly ensures you don’t damage other components.

2. Faulty Speed Sensor

A malfunctioning speed sensor makes Peterbilt 379 truck’s speedometer cease functioning or provide inaccurate readings. The speed sensor is an essential component. It transmits signals to the speedometer gauge, indicating the truck’s speed.

A malfunctioning speed sensor  speedometer  provide inaccurate readings

A faulty speedometer sensor can be detected if:

  • The speedometer gauge fluctuates
  • Shows wrong readings

Sometimes, checking engine lights may also turn on if it is faulty. As a result, if it malfunctions, the system won’t be able to measure or determine the speed, prompting the speedometer to stop working properly.

Solution to malfunctioning speed sensor

The issue can be fixed through sensor replacement. Here’s how:

  • Find the speed Sensor: It is usually located near the drive shaft on the transmission.
  • Unplug the Sensor: Disconnect the wires by unplugging the connector.
  • Remove the Old Sensor: Use a wrench to remove the old sensor from the transmission.
  • Install the New Sensor: Place the new sensor in the same position as the old one and tighten it with a wrench. Then, plug in the connector.
  • Test the Speedometer: Start the motor and verify if the speedometer is working properly.

If you need more help, this video can guide you. Use a reliable website to purchase the sensors if you need any replacements.

3. Faulty Engine Control Module

A defective engine control module can also result in this issue in the Peterbilt 379 truck. The ECM regulates various structures in your Peterbilt truck, including a speedometer. A faulty ECM results in speedometer issues, including:

A faulty ECM results in speedometer issues
  • Reading inaccurate speed
  • Stopping working altogether
  • Providing inconsistent measurements

It tracks multiple facets of your truck, such as:

  • Ignition timing
  • Fuel and air mixture
  • Speed

If this unit or transmission malfunctions, the truck may fail to detect its moving speed and will remain at zero for extended periods.

If the engine is not working properly or stalling shortly after ignition, the culprit may be the control module. Additionally, inspect for overheating of the unit as it indicates a potential issue.


The ECM is costly and intricate. Replacing it demands expertise and proficiency. If you lack these skills, sticking solely to visual examination would be preferable.

Get in touch with a mechanic and have them repair the issue. Once replaced, start your truck to check if it’s functioning.

4. Blown-Out Fuse

A speedometer can burn out due to an electrical overload or a short circuit. When this occurs, the speedometer will stop working.


Replacing is an easy process. To do this;

  • Find the speedometer fuse on your truck. Usually found in the instrument cluster. Consult the owner’s manual for the exact location.
  • Turn off the engine and disconnect the negative battery cable to avoid electrical hazards.
  • Remove the blown-out fuse and install a replacement matching the current rating. Make sure you insert the new one correctly.
  • Reconnect the battery cable and start the engine. Check if the speedometer is working.

If the speedometer remains non-functional, the issue may lie with the wiring, speed sensor, or instrument cluster. Having a professional mechanic diagnose and solve any sensor problem is best.

5. Change the Faulty Speedometer

If you have tried all the solutions and the problem persists, you are dealing with a faulty speedometer. Replacing the entire instrument cluster is complex, and you must be careful while performing it.

If you have tried all the solutions and the problem persists, you are dealing with a faulty speedometer

If the cluster needs to be replaced, it’s best to contact a mechanic or a truck repair shop. Contact Peterbilt’s customer service team if the warranty hasn’t expired. By doing this, you can obtain a replacement while paying the least out of your pocket.

Triggers of Peterbilt Speedometer Malfunction

There are several potential causes for a Peterbilt speedometer to malfunction. Here are some of the most common:

  • It can fail to work due to a problem with the speedometer sensor, cable, or gauge.
  • The check engine light might be on if there is a faulty speed sensor.
  • A loose connection in the wiring harness is another potential issue that needs to be looked at by a mechanic.
  • An instrument cluster that is malfunctioning is another potential cause of this.
  • The computer sends signals to the gauges, so if it isn’t working, the gauges won’t either.
  • Electrical problems such as loose wiring can disrupt the signal between the speed sensor and the speedometer.
  • The speedometer may not display the correct speed if it is incorrectly calibrated.
  • Worn-out gears, damaged bearings, or a broken speedometer head can also cause it to malfunction.
  • The circuit board that controls the instrument panel can also develop issues.

Repairing a Malfunctioning Peterbilt Speedometer and Speed Sensor

Here are some ways you can take to fix a faulty Peterbilt speedometer:

  • Occasionally, changing the cable will resolve a speedometer problem caused by a cable issue.
  • By changing the speedometer sensor and inspecting the wiring harness, speedometer display issues can be resolved.
  • An unreliable gauge can be fixed so that it is no longer an issue by installing a new instrument cluster.
  • If the truck’s transmission is the cause of the speedometer not working, there may be additional issues with the vehicle that need to be addressed by a mechanic.
  • A broken instrument cluster typically needs a replacement.

Diagnosing a Faulty Peterbilt Speedometer Cable

You can perform a few simple checks to know if the Peterbilt speedometer cable is bad.

If you have tried all the solutions and the problem persists, you are dealing with a faulty speedometer
  • You can detect a faulty speedometer cable moving manually. A replacement should be made as soon as possible if there is a lot of play in it.
  • The speedometer cable likely needs to be replaced if it is not picking up any data.
  • A sensor or a wiring harness issue could cause inaccurate speedometer readings. Ensuring that your browser and computer are working can help prevent issues with your Peterbilt.
  • A new cluster will likely need to be installed if the speedometer’s functionality remains unchanged.


Can a Speedometer be Fixed?

Yes, a speedometer can be fixed. If the speedometer is not working properly, it could be due to a malfunctioning speedometer wire or cable or a problem with the speed sensor. A professional mechanic can diagnose the issue, fix it or replace any faulty components.

Why Won’t My Speedometer Needle Move?

Your speedometer needle won’t move because of a faulty speedometer cable, defective sensor, or a problem with the speedometer gauge.

Is Peterbilt Owned by Ford?

No, Peterbilt is not owned by Ford. Peterbilt is a division of PACCAR Inc, a global technology leader in designing, manufacturing, and customer-supporting high-quality trucks under the Kenworth, Peterbilt, and DAF brands.

What is so Great About Peterbilt?

Peterbilt trucks are known for their durability, reliability, and performance. They are designed to provide maximum efficiency and productivity while delivering exceptional comfort and safety to drivers. They are also highly customizable, allowing customers to choose various options to tailor their needs and preferences.

How Much HP Does a Peterbilt 379 Have?

The horsepower of a Peterbilt 379 can vary depending on the engine and configuration of the truck. However, the Peterbilt 379 is typically powered by a Caterpillar C15 engine, producing up to 550 horsepower and 1,850 lb-ft of torque.


A malfunctioning speedometer can be a serious issue for truck drivers. It’s essential to address it promptly for your safety, by using the advice upper.

Have you ever had to deal with a faulty speedometer in your vehicle? Comment below on what caused the issue and you resolved it.

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