BELL 6L7204 - Caterpillar

Illustration 1 g01042208There are two transmission output speed sensors located in the top of the output transfer gear case. These speed sensors are frequency sensors. Frequency sensors produce a signal (Hz) which varies as the condition changes. The transmission output speed sensors receive power from the Power Train/Chassis Electronic Control Module (Power Train/Chassis ECM). The sensors generate an approximate sine wave signal from the gear teeth of the transmission output gear as the gear teeth pass the sensors. The sensors produce a signal that equals one pulse per gear tooth. These signals are sent to the Power Train/Chassis ECM. The Power Train/Chassis ECM measures the frequency of the signals in order to determine the ground speed of the machine.The information from the transmission output speed sensors and the information from the shift lever position sensor allow the transmission to automatically shift while the ground speed changes. The transmission will automatically shift until the information from the transmission shift lever position sensor signals the Power Train/Chassis ECM to stop the automatic shifts.The transmission will not shift into a higher speed than the speed that is selected on the transmission shift lever. During overspeed conditions the Power Train/Chassis ECM will unlock the torque converter.When the signals from the transmission output speed sensors indicate a downshift, the Power Train/Chassis ECM will automatically downshift.Note: The speed sensors are used to diagnose each other during normal operation. The Power Train/Chassis ECM periodically checks the value from the speed sensors. If an incorrect value is found, the Power Train/Chassis ECM will log a service code that indicates a fault for a speed sensor circuit.Reference: For more information on diagnostic operations of the power train electronic control system, refer to Systems Operation, Troubleshooting, Testing and Adjusting, Power Train/Chassis Electronic Control System, "Diagnostic Code List".