Automotive Diagnostics — Overview

Now that we know a use case for diagnostics in the auto industry, we should be in a good place to understand the technical details behind diagnostics.

So, we know that every CAN message has an ID associated with it, and the lower the ID, the higher is the priority of the message which indicates the higher is the importance of the information being communicated in the message. Diagnostics usually have two message IDs associated with them. One for request, one for a response. What do we understand by this? If the client (Tester tool by the service technician) requests for information from the server (The ECU) in the request CAN message, the ECU processes the request, consolidates the information, and responds back with either a positive response, negative response or no response (If the message is not intended to the ECU) in the response CAN message. With this, it can be understood that diagnostic message communication follows a client-server model.

PARTS OF A DIAGNOSTIC MESSAGE

REQUEST MESSAGE

A request message consists of 3 parts

• Request Service ID — The part of the message which lets the ECU know to perform a particular service
• Sub Function (applicable for certain request Service IDs only) — Specific Details of the service…