Use this library and schematics for sniffing purposes

[anyzunstudios]

Hello, first of all thank you for your excellent project, which makes communication between the car and Arduino much simpler.

I am currently working on an ’03 Lexus IS200 XE10, which uses the ISO9141-2 protocol with 5-baud initialization for diagnostics.

My goal is to use Arduino to sniff the communication between a diagnostic tool and the vehicle, in order to read some PIDs related to the ABS status (I would like to trigger the turn signals whenever the ABS activates during an emergency brake).

I already know that with a diagnostic tool I can read the ABS activation state.
My question is: using the provided schematic with transistors and resistors, together with this library, is it possible to sniff the communication between the diagnostic tool and the ECU? Or could this setup cause interference on the K-Line?

Thanks in advance!

[muki01]

This project was designed to get general information from the ECU, and this method works the same way on most cars. However, if you want to connect to other special modules, each car uses different codes, so I cannot tell you exactly what codes to use. You can figure it out by sniffing the communication.

Yes, it is possible to sniff the communication using this library and schematic. However, if you want to connect through the OBD2 port, it works in a request/response manner, so you will only see data if you send a request.

The other method is to connect directly to the wires between the modules, which should allow you to see the data without sending requests.

You can also sniff from the OBD2 port. For example, if you have a professional diagnostic tool, you can connect it and your device to the OBD2 port at the same time. Then, you can observe which codes the professional tool sends to request data from certain modules and read those with your device. But this method can be quite tedious.

Normally, I’ve tried sniffing from a professional tool via the OBD2 port, and it works perfectly, although it’s a bit complicated. I haven’t tried the direct wiring method, but it should work as well.

[jorlandobr]

The easiest and cheapest way to sniff an OBD port is using an USB logic analyzer compatible with Saleae devices. For analyses, Pulseview or Saleae Logic.

Remember that the probe support TTL level signals (5V max) omly, so use a voltage divider to probe the OBD port signals (12V)