INSTALLATION 3C8480 - Caterpillar

Illustration 1 g01192564
Schematic of the Speed Sensor (Transmission Output)This diagnostic code is recorded when the ECM receives an incorrect signal from the speed sensor. The signal is below the dropout signal level. The engine must be running. The incorrect signal that is being read by the ECM has the following characteristics: erratic, intermittent and incorrect. The ECM can determine that a problem exists by comparing the signal data. The ECM compares the two signals from the speed sensors. The ECM checks if one of the two signals is invalid or out of the range.One of the following conditions must be present before the diagnostic code will be active:
The signal from the transmission output speed sensor to the ECM is incorrect.Test Step 1. CHECK THE SENSOR RESISTANCE.
Turn the key start switch and the disconnect switch to the OFF position.
Disconnect the machine harness from the speed sensor.
At the connector for the speed sensor, measure the resistance between the two contacts of the connector of the speed sensor.Expected Result:The resistance measurement is between 1000 ohms and 1200 ohms. Results:
OK - The speed sensor has not failed. Proceed to test step 2.
NOT OK - The speed sensor has failed.Repair: Replace the sensor. Adjust the speed sensor properly during the installation. See Testing and Adjusting, "Speed Sensor (Transmission Output) - Replace".STOPTest Step 2. CHECK THE SIGNAL CIRCUIT FOR AN OPEN IN THE MACHINE HARNESS.
Place a jumper between the two contacts of the machine harness connector for the speed sensor.
Disconnect connectors J1 and J2 from the machine harness of the ECM .
Measure the resistance from the sensor signal J1-6 wire (710-GN) to the return contact J1-7 wire (E987-WH) of the machine harness.Expected Result:There should be continuity (less than 5.0 ohms resistance). Results:
OK - The signal circuit in the machine harness is correct. Proceed to test step 3.
NOT OK - There is an open in the signal circuit of the machine harness.Repair: Repair the machine harness or replace the machine harness.STOPTest Step 3. CHECK THE SIGNAL FOR A SHORT.
Remove the jumper between the two contacts of the speed sensor of the previous test "CHECK SIGNAL CIRCUIT FOR AN OPEN IN THE MACHINE HARNESS".
Reconnect the machine harness to the speed sensor.
At the J1 and J2 harness connectors, measure the resistance between J1-6 (wire 710-GN) and all sources of positive voltage and ground.Expected Result:Each resistance should be greater than 5 ohms. Results:
OK - The machine harness is correct. Proceed to test step 4.
NOT OK - There is a short in the machine harness.Repair: The short is between the signal circuit (wire 710-GN) and the circuit with the low resistance measurement. Repair the machine harness or replace the machine harness.STOPTest Step 4. CHECK IF THE DIAGNOSTIC CODE REMAINS.
Clean the contacts of the harness connectors.
Reconnect all harness connectors.
Turn the disconnect switch and the key start switch to the ON position.
Start the engine. Place the machine in first gear and move the machine.
View the status of the diagnostic code. The diagnostic code is active or the diagnostic code is NOT