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CAN Sniffer: Data Sniffer for CAN Bus Messages
All modern vehicles today are controlled by multiple Electronic Control Units (ECUs), which you can think of as small computers controlling all electrical components in your car.
Using the OBD-II port and an AutoPi it is possible to communicate with the ECUs.
One of the ECU’s is called the Engine Control Module (ECM). This is responsible for communication with a lot of subsystems, like transmission, power steering, windows and doors.
These subsystems communicates on a network bus called Controller Area Network (CAN), by broadcasting messages on the bus. A message could look like this:
- From the AutoPi Cloud, start CAN monitoring
- In your car, perform the action you want to record 5 times or more
- Let AutoPi Cloud analyze the recorded data in order to identify your action
- Name and save the action in the AutoPi library for everyone to use in the future
What is CAN Bus Sniffer?
CAN Bus Sniffer is a control unit that injects data on the CAN Bus through the device plugged in the vehicle. It can be a Telematics Unit plugged in through the OBD-II port to transfer raw CAN Bus messages into a readable form. It is an advanced function and you can usually discover plenty of hidden functions in your vehicle.
CAN Bus Sniffing is a very helpful functionality and can reveal several hidden functionalities, as well as prolong your vehicle lifespan. Typically, it requires advanced technical expertise, but not in our case. We have made it simple and usable by anyone interested in the functionality.
CAN bus sniffing explained
Monitoring the CAN Bus is complicated, because
so much data flows in modern cars. So identifying individual
messages from the stream of data is difficult.
You can apply this to finding CAN messages as well. Let's say you want to discover the command for controlling the power windows, then the steps involved are:
- Record messages flowing while pressing the window switch in the car.
- Divide the recorded messages into two halfs.
- Replay/send all data from one part to the car’s CAN Bus. If the window rolls down you have the right part.
- Keep doing this procedure until you have identified the exact message you are looking for.
Once you identified the specific command, you need to replay/send it to make sure you have the right
one.
All of this sounds very complicated (which it can be), but with AutoPi all of this has been automated in a
simple tool you can access from the AutoPi Cloud. The AutoPi Telematics Unit can be considered as a CAN Bus
Sniffer due to its wide variety of functionalities it offers.
Benefits of CAN bus reverse engineering
CAN bus reverse engineering has lots of benefits, however, we will tell you more about the most common ones.
- Decoding data - also known as CAN bus hacking, stands for the ability to enable decoding of proprietary CAN IDs. Then it is able to analyze data from cars, trucks, machinery and so on.
- Give commands - you are able to give commands to your car. This can be done by enabling control of vehicles via commands such as toggle locks, lights and so on.
- Applications - You are able to log state-of-charge (SoC) from electric vehicles (EV).
- DBC databases extension - CAN bus decoder tool can definitely help you with reverse engineer missing CAN messages and signals.
CAN bus reverse engineering brings you lots of useful lifehacks, that's why it is also called CAN bus hacking. Read more about it below and find out how can AutoPi help you with CAN bus in your car.
Using AutoPi to discover new commands in my car
With the AutoPi Cloud Management Platform, the tedious process of finding CAN commands for your vehicle has been automated in a simple user interface.
Above image shows the user interface used to discover new CAN commands. The steps are very simple. You need to physically be in your car to do the discovery:
- Open the CAN explorer. It will tell you if there is connection to the car
- Press the record button
- Now perform the function you want to record 5 times. Like pressing the “left front window” switch
- Press the stop record button
Using discovered CAN commands to build something cool
So, what can you do with your new CAN command? Why not use it to tie up a cool speech command to your car.
The AutoPi Cloud comes built in with an If-This-Then-That trigger system. Using this system you can add your
own triggers and trigger the new found CAN command.
- Select your input source. This is the beacon. As an example select the “googleAssistantSpeech” source
- Add a critearia, this is the text spoken. We will add “Roll down left front window”
- Now you add your output source. this is the reactor. We select the “carIntegrator” and from the dropdown menu, we find our new command “left front window down” and select this
- Press save