GMLAN sniffing with Arduino + MCP2515 board

If you are reading this I suppose you are already familiar with GMLAN. In short, GMLAN is a communication protocol based on CAN-BUS to send data between different Electronic Control Units (ECUs) in the car like BCM (Body Control Module), IPC (Instrument Panel Cluster), EHU (Entertainment Head Unit) and so on. GMLAN is a single-wire CANBUS protocol (SWCAN) with 33.3kbps baudrate.

The only thing I wanted was to sniff steering wheel radio commands and send them to control my CarPC, but this turned out very interesting for me to think of other possibilities and ways to make my car smarter.

On previous posts you can see that I have an Opel/Vauxhall Corsa D which is an GM (General Motors) car. I have a spare instrument panel cluster (IPC) I bought months ago just laying around, doing nothing. I never installed it in my car as it is incompatible and needs programming with an expensive programmer which I don’t have. So, I wanted to try sniffing the GMLAN and find out the commands to start-up and control the instrument panel cluster.

For this project, I’m using Arduino Nano with MCP2515 controller and TJA1040 transceiver module. If you have 8MHz crystal oscillator on the MCP2515 board I would suggest changing it to 16MHz. Below is the wiring schematic:

Connect CANH to GMLAN wire and CANL to GND. Interconnect grounds from Arduino, to MCP2515 board and your car or module you want to sniff messages from.
Next step is loading MCP_CAN_lib library in Arduino IDE. Before trying to send messages, I would suggest first trying to read. In the library examples load the file named CAN_receive.
For sniffing GMLAN Low Speed CANBUS, adjust baudrate to CAN_33K3BPS.

Upload the code, turn on your car or module and start the Serial Console from Arduino IDE. You can also use PuTTY or Realterm if you are using Windows, or if you are using Linux, you can just type screen /dev/ttyACM0 or screen /dev/ttyUSB0.

I found the commands for starting up the IPC, rev and speed gauges, turn signals and chime.

I used CAN_send example loaded with the appropriate commands and sent them to the IPC.

See it in action:

8 thoughts on “GMLAN sniffing with Arduino + MCP2515 board

  1. LeoDJ

    Wow! Awesome project!

    In fact, I’m currently trying to read the steering wheel controls as well, but I don’t quite have the experience with CAN.

    Would you mind sharing the Arduino code for the CAN sniffing, or even better the CAN codes for reading the steering wheel controls (if you found them already, if not, the codes for the IPC would also be interesting)

  2. FB

    Awesome project, cant wait for it.

    I want to do the same with my astra h cd30, so i will be here waiting xD

    keep up the good work!

    1. Dimitar Post author

      Thank you for your comment! I’m currently busy with planning and rebuilding my workshop, when I finish I will continue this project.

  3. Ray Nixon

    WOW, i have been playing with LOW Speed GM-LAN for the past few days…

    i have my arduino and MCP2515 all set up… i am trying to do something very similar to you actually…

    i have a instrument gauge that is from a slightly newer model car than what i have and I’m trying to send the appropriate can message to control the gauge… only problem is, using the same library you are using i cannot get a send command to work. i have the can initialised and running at 33.3kbps…

    the only thing is i am not using the TJA1040 transceiver. is it a must?

    1. Dimitar Post author

      Are you using MCP2515 module for Arduino? If you do, check the oscillator/crystal, and if it is 8MHz, change it to 16MHz. That board already has the transciever TJA1040 built-in. Connect instrument cluster ground to CANL and Arduino GND, and GMLAN Wire to CANH.

      1. Ray Nixon

        yeah I’m using the MCP2515 module… i have ordered the 16MHz crystal… hopefully that fixes my problem. cheers for the reply.


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