What is a VSS wire? VSS is an acronym for vehicle speed sensor, and its wire is responsible for transferring the VSS signals to the electrical control module.
This module uses this input to run other subsystems, such as cruise control, fuel injection, ignition timing, navigation, and torque converter lockup.
So let’s define this component by defining the vehicle speed sensor.
Table of Contents
- What is a VSS?
- Purpose of the Vehicle Speed Sensor Wire
- Symptoms of VSS Wire Failure
- Wrap Up
What is a VSS?
As stated earlier, VSS is a vehicle speed sensor. It can be between the wheel and axle to measure wheel speed or at the rear section of the transmission to measure the transaxle or transmission output.
The speed sensing function can occur in two ways, which define the two VSS types.
A vehicle speed sensor
Hall Effect VSS
This sensor monitors the transaxle’s output on the differential gear housing. It has no moving parts and requires an external source of power.
Also, the system relies on an internal reference voltage signal to time the shaft and wheel’s speed in ABS systems.
As the reluctor fingers on the brake disk rotate against this sensor, they create a magnetic field that activates an internal transistor.
A speed wire transmits this internal transistor voltage to the ABS, which counts the voltage peaks, then divides them by time. The result is the vehicle’s velocity.
A Hall effect sensor module with an internal transistor
With this VSS type, the signal amplitude remains constant and only drops to zero when the reluctors pass.
Hall Effect VSS Advantages
- Reliable (zero moving parts)
- High repeatability
- Pre-programmable with outputs and angles
- Quick response time
- Sufficient sensing distance (less than 21mm)
Hall Effect VSS Disadvantages
- Narrow operating temperature range (-55°C to 125°C)
- Requires a continuous power source and output current exceeding 10mA
- Must be polarity sensitive to avoid false signal triggering
- Current and voltage switching range occurs via an external switch (cannot switch them directly)
Reed Switch VSS
Reed switch sensors are binary mechanical devices consisting of magnets and reed switches.
The speedometer-cable-powered magnet component turns the reed switch on or off approximately four times per full rotation, enabling pulse calculation per second.
This calculation gives the vehicle speed.
A tiny magnetic reed switch module
The continuous magnet rotation also generates a voltage proportional to the rotational speed.
Reed Switch VSS Advantages
- Reed switch sealed from contamination using inert gas
- High repeatability (zero leakages/voltage drops)
- Switches loads directly (up to 2A at 1000V)
- Requires no external protection circuit
- Long lifespan
- Wide operating temperature (-55°C to 150°C)
- Long sensing distance (less than 41mm)
Reed Switch VSS Disadvantages
- Produces more noise than hall effect VSSs
- Can experience wear on the contacts
- High hysteresis
- Slow response time
Purpose of the Vehicle Speed Sensor Wire
This wire transmits the VSS signals to various systems, such as cruise control and some in-dash units.
Let’s focus on the head unit application, where the wire provides signal pulses for the navigation system.
If you remove the OEM radio, you will notice four plug connectors that bring in power and signals.
When installing an aftermarket radio, you’ll only use two of the four connectors, specifically the ones with larger pins.
Car radio wires (this unit has no navigation feature)
Stereo installations don’t require the other two. The VSS wire (brown wire) is usually in one radio harness with a large connector.
But the color code can differ depending on the car’s make and model. For instance, it can be a dark-green-with-white wire or a red-green wire.
In other vehicles, it can be a black wire with a gray stripe (black stripe wire) in the auxiliary harness.
So you need to get detailed information about your vehicle’s wiring diagram and check the radio harness to determine the correct wire that brings in the VSS signal.
Otherwise, the aftermarket stereo navigation system might not work because it won’t detect the vehicle’s movement.
The navigation system will show the maps, but it won’t be able to track your movements and position to give turn-by-turn directions.
A car navigation system
Can You Substitute the Tach Signal Wire With the VSS Wire?
No. Unlike the tachometer signal wire, the VSS wire does not send pulses when the car is at a standstill.
The tach wire transmits signals to the instrument cluster as long as the engine is on.
But the VSS wire halts when you come to a stop. It only sends the signals as a series of 800 to slightly over 1,000 pulses each mile as the car moves.
So using this wire instead of the tachometer wire will make the instrument cluster misbehave.
Symptoms of VSS Wire Failure
VSS wire or sensor failure causes these symptoms.
Cruise Control Failure
Cruise control relies on the vehicle speed sensor to adjust your car’s speed depending on your settings and the car ahead.
If the data signals don’t come in, your cruise control system won’t be able to know your vehicle’s speed.
A car with adaptive cruise control
The powertrain control module also relies on the VSS data to shift gears correctly.
So the vehicle will change gears roughly or more quickly if the VSS wire is faulty.
Also, this failure can extend the shift timing, causing damage to the gearbox’s internal parts.
Check Engine Light Turns On
A check engine light turning on can mean several issues, one being a transmission/vehicle speed sensor issue.
You can scan your vehicle using an OBD-II scanner or take it to a mechanic to confirm the source of the error.
The universal check engine symbol
A vehicle speed sensor is critical, but it is only as good as the wire that links it to the components that need the speed signal.
So check the VSS wire if you notice failures in the cruise control, gear shifting, navigation, and other systems that require speed settings.
And contact us if you can’t locate this cable. We’ll be happy to help.