In this blog post, we'll talk about the two most common types of wheel speed sensors and how they affect your project, especially in relation to the ABS (anti-lock braking system). It's worth noting that there is a difference between wheel speed and vehicle speed. Check out the end of this post for more about vehicle speed.
What is a Wheel Speed Sensor?
A wheel speed sensor is the sensor attached to a hub (where the wheel and axle meet) that determines how fast the wheels are spinning and sends that information to the ABS.
Why Does it Matter if My Wheel Speed Sensor Works?
If the wheel speed system is not sending the correct information, the ABS will not work. This is less of a problem in older cars since ABS may or may not matter to you, but for cars equipped with CANbus, this means losing the ABS and the vehicle speed, which will lead to a domino effect of other systems not working as intended. This is why it's important to ensure the correct replacement part and sensor when doing a hub swap in your project.
Wheel Speed Sensor Types:
Older type sensor - non CANbus
These wheel speed sensors are found on older hubs from non-CANbus-equipped vehicles with matching ABS units. The sensors themselves change around a little bit from year to year but they all have the same waveform output that the ABS module picks up. They have a waveform that looks like the one below.
The following models would come with this type of wheel speed sensor:
1992-2004 Legacy (all models)
1993-2007 Impreza (includes OBS)
1997-2004 Outback (all models)
1998-2008 Forester (all models)
2002-2007 WRX
2003-2006 Baja (all models)
2004-2007 STi
Newer type sensor - CANbus
These wheel speed sensors come from CANbus-equipped vehicles with different ABS systems which many times includes VDC (vehicle dynamics control). Given the switch over to Subaru's Global Platform around this time, the sensors and tone rings should all be pretty much identical, with a few exceptions.
The following models would come with the newer wheel speed sensor type:
2005 - Current Legacy (all models)
2005 - Current Outback (all models)
2005 - 2014 Tribeca
2008 - Current Impreza
2008 - Current WRX
2008 - 2021 STi
2009 - Current Forester (all models)
2013 - Current Crosstrek
2013 - Current BRZ
Hub Swaps - Match Hub and Axle Type!
The problem is that if you switch to a hub or axle that is not the same type as the current one, you will lose wheel speed for that hub because the output waveform is not what your ABS module expects.
Usually hub swaps come in combination with a transmission swap. It's important to maintain the hub style that matches your chassis type. So if converting from 5x100 to 5x114, you'll need to make sure the hubs come from a matching CANbus or non-CANbus platform to work correctly with your chassis and to match the axles to those hubs.
We have people who want to convert their 5x100 hubs from older cars to newer types for easier service, but the problem is that the waveform issue is still in play. The result of doing this is you will lose wheel speed, which means the ABS will no longer work. We would not recommend doing this because there isn't a known solution.
Wheel Speed Sensor Harness and Connectors
The CANbus-equipped models should use all the same connectors, so not much to worry about there. For the non-CANBus cars, there are a few variants in connector type but since all pick up the same pulse, you can use the wheel speed sensor harness that matches the hubs and if it doesn't match the chassis, modify the connector on either side to get things to match up. We carry these connectors if you need them in the link below.
As long as you keep these things in mind when working with hub changes, you'll be good to go!
Vehicle Speed can either come from the transmission on older cars or from the wheel speed sensors, through the ABS module and sent to the rest of the car via the CANbus network for newer cars. More on vehicle speed sensors and CANbus can be found in the links below.
If you are installing a transmission that does not have a vehicle speed sensor built into it, but the car receiving the transmission originally had a built-in speed sensor (aka new transmission in older chassis), please take a look at the VSSPro.
