Shift Solenoid: Description and Operation

The ECM uses the signals from the throttle position sensor and Air-flow meter to monitor the engagement condition of the lock-up clutch.

Then the ECM compares the engagement condition of the lock-up clutch with the lock-up schedule in the ECM memory to detect mechanical trouble of the shift solenoid valve SLU, valve body, torque converter clutch and automatic transmission assembly.

Shift solenoid valve No.4 is controlled by ECM and it switches ON and OFF of the O/D direct switch.


Shifting from 1St to 5th is performed in combination with ON and OFF of the shift solenoid valves No.1, No.2 and No.3 controlled by ECM. If an open or short circuit occurs in either of the shift solenoid valves, the ECM controls the remaining normal shift solenoid valve to allow the vehicle to be operated smoothly (Fail safe function).


The ECM uses signals from the vehicle speed sensor and input/turbine speed sensor to detect the actual gear position (1st, 2nd, 3rd, 4th or 5th gear). The ECM then compares the actual gear with the shift schedule in the ECM memory to detect mechanical trouble of the shift solenoid valves, valve body and automatic transmission assembly.