Automotive Diagnostics — Link Control

This service is used to control the communication between the client/tester and server/ECU. This is generally done to gain bandwidth for any diagnostic communication. There can be an option to change the CAN data link layer parameters during a non-default session

The client verified if the ECU supports a particular mode transition mechanism. The client can request for the change in data link parameters only if there was a positive response when the client requested the mode support request previously.

Important points about Link control service

• This service can be executed only in a non-default session
• The service switches the parameters to default mode when the session is transitioned back to the default session

Sub-functions supported by link control (0x87) service are

Message Flow Examples

Let’s consider a scenario where the client is requesting the server to transition the baud rate to a fixed baud rate

Know that 0x05 refers to a baud rate of 115200Baud

Request Message to verify Mode Transition With Fixed-Parameter

Positive response

Message Request from client to Transition the baud rate

Positive response from the server for mode transition request

Negative response code from the server

Supported negative response codes