Sessions

UDS operates through diagnostic sessions, which are states in which the ECU operates to perform specific diagnostic or service functions. Each session provides a different level of access to the ECU’s functionality. The ECU starts in a default session, but diagnostic tools can request transitions to other sessions to perform specialized operations.

Types of UDS Sessions

1. Default Session (0x01), class ApplicationDefaultSession.

   • Description: This is the basic session active upon ECU startup.

   • Functionality: Limited diagnostic services are available, primarily for querying information (e.g., ID requests, DTCs).

   • Typical Use Cases: Basic diagnostics, reading fault codes.

2. Programming Session (0x02), class ProgrammingSession.

   • Description: Used for reprogramming the ECU firmware.

   • Functionality: Enables downloading new software or calibration data into the ECU.

   • Typical Use Cases: ECU flashing, firmware updates.

3. Extended Diagnostic Session (0x03), class ApplicationExtendedSession.

   • Description: Provides enhanced diagnostic functionality beyond the default session.

   • Functionality: Includes advanced capabilities like actuator testing, detailed fault code analysis, and special function testing.

   • Typical Use Cases: In-depth diagnostics, calibration, and testing.