CANBUS in your Subaru Explained
Updated: Aug 9, 2019
What is CANBUS?
CANBUS or Controller Area Network Bus is a communication system for your car. It uses digital signals compared to analog signals found in older cars.
Digital (CANBUS) vs. Analog
This system uses simple voltage or ground to tell the device its status. This means there is a signal being sent to an independent spot or "node" at a module (like an ECU) which will give the module specific information about that particular sensor. Think of this as a text message direct to you from a single sender, a one on one communication. For example, on an analog gauge cluster each input (check engine light, speed, ebrake, etc) all have individual wires to feed information to the cluster. Below is a diagram from an 04 WRX that uses an analog cluster. Notice how each input corresponds with a single location on the cluster.
CANBUS utilizes a single pair of twisted wires that connects all of the modules together and information is being passed around all at once with 0s and 1s (think computer code). Each individual message has an ID so that as it moves through each module, the module can either pick up the ID and do something with it or if it's not looking for that ID it just ignores it. Think of a group chat where everyone is speaking all at once carrying on different conversations. The only way you can pin point something important to you is if someone tags your name to grab your attention. For example, on a CANBUS cluster many of the inputs (check engine, speed, ebrake, etc) come through the same pair of wires and the cluster filters each input based on it's unique ID and displays on the cluster accordingly. Below is the cluster from a 2015 STi. You can see all of the different inputs come in through pins 32 and 33 and head into the CAN transceiver and receiver to be filtered. Keep in mind that the cluster is also sending info out on the CAN line so this is a two way street of inputs and outputs.
Why did vehicle manufacturers switch to CAN bus?
Engineers have switched to this method of communication because you can add a lot more complexity and communication to your wiring and electronics systems without adding more wire. This is great for more features in your stock car but does make it much trickier to do your Subaru swap.
How does CAN bus effect my Subaru swap?
The problem with swapping your CANBUS Subaru engine into another car is that the ECU is not happy when it doesn't receive all of the proper inputs from all of the modules in your car (immobilizer, gauge cluster, ABS, etc). The ECU needs this information from the CAN line to properly function and run the car. We will go into the details of how to get around this when swapping your car in a future blog post.
How do I know if the car/engine I plan to swap has CAN bus?
The best way to tell if your car or engine is CANBUS equipped is by the model and year of the car. Below is a list of CANBUS equipped cars. All cars older than this list are NON CANBUS (Analog).
CAN Bus Cars:
2005 to current Legacy
2008 to current Impreza
2009 to current Forester
*Note - for the Legacy GT CAN bus started in 2005 so beware when looking at these engines because they are inexpensive to purchase but they are not a great replacement for NON CANBUS equipped cars.