PIN 7P6984 - Caterpillar

Illustration 1 g03095896
(1) Engine output speed sensor (2) Torque converter output speed sensor (3) Transmission output speed sensorsEach speed sensor has two connections to the ECM (+ and −). For all of the speed sensors, connector contact "2" is the signal line and connector contact "1" is the return line. The speed sensors send an AC frequency signal (HZ) that matches the number of gear teeth passing the sensor per second to the ECM. The ECM compares the frequency from the speed sensor (HZ) to the number of pulses per revolution in order to determine the speed of the rotating components. The ECM uses the input from the speed sensors in order to regulate transmission shifts.The speed sensors are used to cross check and diagnose each other during normal operation. Cross check uses two transmission output speeds and the torque converter output speed. These speeds will validate and determine which transmission output speed sensor to use for shifting. Cross check compares the three speeds. If at least two speeds agree, the transmission shifts as expected. Otherwise shifting is inhibited and the lockup clutch is disengaged. The ECM periodically checks the value from the speed sensor. And if an incorrect, erratic, or absent value is found, the ECM will log a service code (speed sensor diagnostic) that indicates a fault for a speed sensor circuit.There is one engine output speed sensor (1), one torque converter output speed sensor (2), and two transmission output speed sensors (3). These sensors are all on the straight through transmission. All speed sensors are used to determine if any individual speed sensor has failed.