How to Replace a Vehicle Speed Sensor

issan 240SX Rear Differential with the Vehicle Speed Sensor sticking out of it.
Wikimedia Commons

Modern vehicles are monitored and controlled by many sensors and actuators, all communicating with a few computers. The vehicle speed sensor is just one of many in the modern vehicle, and may provide vehicle speed information to many systems. These may include the engine control module (ECM), transmission control module (TCM), cruise control module (CCM), anti-lock brake system module (ABS), and instrument cluster module (ICM), to name a few.

Most vehicles use a transmission-mounted vehicle speed sensor, while some vehicles, usually older models, use a cluster-mounted speed sensor. Transmission-mounted VSS are purely electronic, sensing a transmission tone ring or running off a gear inside the transmission. Cluster-mounted VSS are run by a flexible cable from the transmission, converting that rotary signal into a digital signal. There are a couple reasons you might have to replace a vehicle speed sensor.

Why Might You Have to Replace a Vehicle Speed Sensor?

The check engine light is usually one of the first indicators that you have a VSS problem. A scan tool diagnosis might recover a diagnostic trouble code (DTC) such as P0720, P0721, P0722, or P0723. The vehicle speed sensor (VSS) isn’t to be confused with a wheel speed sensor (WSS), and it does one good to note that some vehicles do not have a VSS, even if a module is stating a VSS fault – those are usually circuit or module faults, as vehicle speed is calculated from the wheel speed sensors.

On some vehicles, the speedometer gets its signal from a dedicated VSS. If you notice erratic speedometer function or the speedometer doesn’t work at all, this could indicate a problem with the vehicle speed sensor or the circuit going to it.

If the VSS isn’t working properly, you may note other problems with the vehicle.

The automatic transmission may not feel like it’s shifting properly, cruise control may not function, or electronic stability control warning lights may come on.

Once you’ve done your circuit checks with a multimeter and determined the VSS to be faulty, then replacement is the only option. Only be sure to double check the circuit before condemning the sensor, or else replacing a non-defective sensor will be a waste of time and money.

DIY Auto Repair – Replacing a Vehicle Speed Sensor

The vehicle speed sensor is usually located on the transmission – look at a diagram specific to your vehicle to be certain (Here’s one for Honda Accord). Here are some basic steps to help you replace a faulty VSS on your vehicle:

Transmission VSS – Replacing an externally-mounted vehicle speed sensor is usually simple, held in by one or two small bolts or threaded into the transmission housing. At the very least, you’ll need a couple basic hand tools and a rag for cleanup. Depending on the location of the VSS, you might have to remove covers or other parts to get to it. If you need to lift the vehicle to access the sensor, use proper lifting procedures and always support the vehicle on jack stands – never put any part of your body under a vehicle supported only by the jack.

  1. Disconnect the electrical connector and put that out of the way.
  2. Use a wrench or socket to remove the bolts. Screw-in types require a larger wrench. Use penetrating oil if the bolts are stuck.
  3. Remove the sensor. Use penetrating oil and wiggle the sensor to work it loose.
    • If the VSS is located high on the transmission, you probably don’t have to worry about much transmission fluid escaping. Simply use a rag to clean up any drips.
    • If the VSS is located low on the transmission, a good quantity of transmission fluid may escape when you remove it. Use a clean drain pan to capture any lost fluid.
  4. Coat the new VSS’ O-ring or seal with transmission fluid and reinstall.
  5. Any fluid captured during the removal process should be put back into the transmission before running the vehicle.

Cluster VSS – If you have a problem with a cluster-mounted vehicle speed sensor, first verify the speedometer cable is working properly.

If the speedometer is working, but the VSS isn’t, then this usually requires replacing the speedometer or the instrument cluster.

After the Repair

After replacing the vehicle speed sensor, clear any DTCs from ECM memory, then test drive the vehicle. First, make a short run around the parking lot or just a short distance, and check for leaks. Then, on a longer test drive, make sure the check engine light doesn’t come back on and speed-related systems are working properly again.