The ECM commands gear shifts by turning the shift solenoid valves "ON/OFF". According to the input shaft revolution, intermediate (counter) shaft revolution and output shaft revolution, the ECM detects the actual gear position (1st, 2nd, 3rd or O/D gear position). When the gear position commanded by the ECM and the actual gear position are not the same, the ECM illuminates the MIL.
Example
When either condition (a) or (b) is met, the ECM detects a malfunction.
- The ECM commands the 1st gear, but the actual gear is 2nd.
- The ECM commands the 2nd gear, but the actual gear is 1st.