Actuators are devices controlled by vehicle ECUs that perform physical actions, such as activating cooling fans, fuel pumps, fuel injectors, EGR valves, or the electronic throttle body. During the diagnostic process, actuator tests help technicians verify the proper operation of these components, identify wiring faults, and confirm whether the ECU is sending the correct commands. These tests are essential for accurate troubleshooting and help prevent unnecessary replacement of parts.
However, in most modern vehicles, actuators cannot be activated while the ECU is in the default diagnostic session. It is usually necessary to enter an Extended Diagnostic Session (UDS Service 0x10 03) because these functions can directly affect vehicle operation and must be protected for safety reasons. In some cases, additional security mechanisms such as Security Access (0x27) are also required. Therefore, understanding the importance of the extended session is essential for technicians and engineers working with advanced automotive diagnostics, as many testing, calibration, and control functions depend on it.
