What sensor causes the speedometer not to work?

The Vehicle Speed Sensor (VSS) on the transmission is the primary source of speed data for most speedometers. In newer vehicles, wheel-speed sensors from the ABS system and data shared over the CAN bus from the transmission or ABS module can also drive the gauge. When the speedometer stops, the most likely culprits are the sensor itself or its wiring, though the instrument cluster can fail too. This article explains the sensors involved and how to diagnose the fault.

The sensor at the heart of the speedometer

In most cars, a dedicated Vehicle Speed Sensor (VSS) on the transmission sends pulses to the ECU and instrument cluster to translate speed. In many modern vehicles, the ABS wheel-speed sensors or data from the CAN bus may be used to generate the speed reading.

Below are the devices and data sources commonly involved in providing speed information to the gauge.

• Vehicle Speed Sensor (VSS): Typically mounted on the transmission; reads the rotation of the output shaft and sends a signal to the engine computer and instrument cluster.


• Wheel Speed Sensors (ABS sensors): In some vehicles, the ABS sensors provide speed data through the ABS control module or CAN network; a failure can cause the speedometer to read inaccurately or not at all.


• Transmission Output Speed Sensor (if separate): Some automatic transmissions use a dedicated sensor on the output shaft feeding the speedometer or ECU.


• Instrument cluster or gauge fault: A bad gauge or corrupted cluster software can produce a non-reading even if sensors are fine.


• Wiring and fuses: Damaged wiring, loose connectors, or blown fuses can interrupt the signal between the sensor and the cluster.

In most cases, the speedometer problem traces back to the VSS or its wiring; if a diagnostic code points to a speed sensor, replacement is often straightforward. If the sensor is fine, the issue may lie in the ABS module, CAN bus data, or the instrument cluster.

How to diagnose a non-working speedometer

Start with basic checks and then move to sensor testing and scanning for codes. The following steps guide you through typical diagnostics.

1. Check for diagnostic trouble codes (DTCs) using an OBD-II scanner. Look for codes related to the vehicle speed sensor (e.g., P0500, P0501, P0720, or manufacturer-specific codes).


2. Inspect the vehicle speed sensor and its wiring: locate the VSS on the transmission, inspect the connector for corrosion, bent pins, or loose connections, and check for damaged wires.


3. Test the VSS signal: with the engine running and the transmission in gear, back-probe the VSS signal wire to see if you get a pulsing voltage or frequency that changes with speed on a multimeter or oscilloscope. Compare to service manual specifications.


4. Check ABS wheel-speed sensors as needed: inspect wheel sensors, tone rings, and wiring; if ABS codes point to a wheel sensor, the problem may be there instead of the VSS.


5. Inspect fuses and instrument cluster power: verify the fuse for the instrument cluster is intact and that the cluster receives power and ground as per the service manual.


6. Test or inspect the instrument cluster: if the sensors and wiring test OK, the issue may be within the gauge cluster or its firmware; some vehicles require dealer-level diagnostics to reflash or repair.

These steps help isolate whether the problem is the sensor, wiring, or the instrument cluster. If you’re unsure, a professional diagnostic with OEM-level scan tools can quickly pinpoint the fault.

Summary

In summary, the speedometer’s data usually comes from the Vehicle Speed Sensor on the transmission. In many modern cars, ABS wheel-speed sensors and CAN-bus data from the ABS module or transmission may supply the speed signal. When the speedometer stops working, start by checking the VSS and its wiring, consider ABS sensor issues, and use diagnostic tools to identify the exact fault for the appropriate repair.

What would cause the speedometer to stop working?

There are many possible reasons why your speedometer might not be working. These include damaged or faulty speed sensors, compromised instrument clusters, gearbox problems, faults in connections and wirings, sensor calibration issues, and vehicle speed sensor (VSS) failure.

What sensor controls the speedometer?

The vehicle speed sensor (VSS) controls the speedometer by measuring the vehicle's speed and sending that data to the car's computer. This sensor is typically mounted on the transmission, but can also be located on the differential or transfer case. The computer then uses the data from the sensor to display the speed on the speedometer, track the odometer, and control functions like transmission shifting and cruise control. 
You can watch this video to learn about the vehicle speed sensor and how it works: 1mAuto V Fix YouTube · Jul 19, 2022
How it works

• Location: The VSS is mounted to the transmission, output shaft, or differential. 
• Detection: It typically uses a magnetic tip to detect a rotating gear on the transmission's output shaft or a magnetic wheel. 
• Signal: As the gear or wheel spins, it creates an electrical signal that the sensor reads. The speed of the signal is proportional to the vehicle's speed. 
• Data transmission: The sensor sends this signal to the vehicle's computer (like the engine control module or ECM). 
• Computer processing: The computer interprets the signal to determine the vehicle's speed and uses this information to control the speedometer, odometer, and other systems. 

This video demonstrates how the speed sensor works and how it can be replaced: 57sNice Guys Garage & Speed ShopYouTube · Sep 25, 2024
Why it's important

• A failing VSS can cause inaccurate speedometer readings, and sometimes erratic speedometer behavior. 
• It is crucial for other vehicle systems, such as the transmission, cruise control, and anti-lock brakes (ABS). 

How do I reset my speed control sensor?

How do I reset my speed sensor? Resetting a speed sensor typically involves either clearing the DTCs or disconnecting the car's battery for a few minutes and then reconnecting it, which can reset the vehicle's computer and clear certain sensor-related issues. What are the symptoms of a failing speed sensor?

Which fuse is responsible for a speedometer?

The fuse that controls the speedometer is typically labeled as the "instrument cluster" or "gauges" fuse, but it can vary by vehicle model. To find the specific fuse, check the fuse box diagrams in your owner's manual or on the fuse box cover itself, as it could be in a fuse box under the dashboard or hood. It's possible there are multiple fuses involved or a less obvious label like "BFC" (Body Function Center).
 
This video shows how to identify and access the speedometer fuse: 23sconquryourfear & do it urselfYouTube · May 7, 2015

• Find the right fuse box: There are often multiple fuse boxes in a vehicle, usually one inside the cabin (e.g., on the driver's side dash) and one under the hood. 
• Look for the correct label: The fuse is most commonly labeled for the "instrument cluster" or "gauges". However, sometimes it may be less obvious, such as "BFC" (Body Function Center) or could be a different number entirely. 
• Check the owner's manual: The most reliable way to find the correct fuse is to consult your owner's manual for the specific fuse box diagram. 
• Inspect the fuse: Once you locate the fuse, check if it has a broken or burnt-out wire inside. 
• Replace the fuse: If the fuse is blown, replace it with a new one of the same amperage rating. 
• Other potential issues: If the fuse is not the problem, the issue could be with the sensor or internal components of the gauge assembly itself.