ELEMENT 4808866 - Caterpillar

Start Switch (Key)
Illustration 5 g00291705
Key Start SwitchThe key start switch is an input of the power train electronic control module (ECM). The key start switch informs the power train ECM of an attempt to start the engine. The power train ECM then initiates the neutral start function. During normal machine operation, the start terminal of the key start switch is open. When the key start switch is turned to the START position, the start terminal closes to the +battery and the +battery voltage is present at connector contact J1-40 of the power train ECM. When all starting conditions are satisfied, the power train ECM sends a +battery signal to the connector contact J1-8 for the start relay and engine cranking begins.Note: After the key start switch is initially turned to the START position, the switch will not return to the START position from the ON position. The switch must be turned to the OFF position first. Then, the switch can be turned to the START position.ReferenceFor more information on the neutral start function, refer to Systems Operation, "Power Train Electronic Control System" for the machine that is being serviced.ReferenceFor more information on the function of the power train ECM, refer to Systems Operation, "Electronic Control Module (Power Train)" for the machine that is being serviced.Sensors
Sensors provide information to the power train electronic control module (ECM) about changing conditions. The sensor signal changes proportionally to the changing conditions. The following type of sensor signals are recognized by the power train ECM.
Frequency signals: The frequency (Hz) of the sensor signal varies as the condition changes.
Pulse width modulated signals (PWM): The duty cycle of the sensor signal varies as the condition changes. The frequency of this signal is constant.
Illustration 6 g00288430
Pulse Width Modulated SignalSpeed Sensors (Transmission and Torque Converter Output)
Illustration 7 g00288428
Speed SensorThere are two transmission speed sensors and one torque converter output speed sensor on the machine. The speed sensors are inputs of the power train ECM. These speed sensors are frequency sensors. Frequency sensors produce a signal (Hz) which varies as the condition changes. The sensor generates an approximate sine wave signal from the gear teeth as the gear teeth pass the sensor. The sensor produces a signal that equals one pulse per gear tooth. This signal is sent to the power train ECM. The power train ECM measures the frequency of the signal in order to determine the speed of the condition. The power train ECM receives signals from the speed sensors. The power train ECM uses the input from the speed sensors in order to determine the speed of the system. The power train ECM uses the input from the speed sensors in order to regulate transmission shifts. Each speed sensor has two connections to the power train ECM (+ and −).The power train ECM sends the speed information to other electronic control modules via the CAT Data Link. For all of the speed sensors, connector contact 2 is the signal line and connector contact 1 is the return