SWITCH AS-PRESSURE 1119563 - Caterpillar

Illustration 1 g02526136
Schematic of the "Speed Sensor (Engine)"
This diagnostic code is recorded when the ECM reads the signal from the sensor and determines that the signal is erratic, intermittent, or incorrect. This is determined when the ECM compares the signal from the engine speed sensor to the signal from the transmission input speed sensor. A diagnostic code is recorded when the signal from the engine speed sensor is below the dropout value and the engine speed is above low idle. This problem prevents the ECM from calculating the ratio of the torque converter. Note: The engine must be running. The engine speed signal must be received from the transmission input speed sensor for the ECM to display this diagnostic code as being present. One of the following conditions must be present before the diagnostic code will be active:
The signal from the engine speed sensor to the ECM is incorrect.
The ECM is NOT receiving the correct information about the engine speed sensor over the data link.Test Step 1. CHECK THE RESISTANCE OF THE SENSOR.
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 110 ohms and 200 ohms.Results:
OK - The resistance measurement is between 110 ohms and 200 ohms. The speed sensor has not failed. Proceed to Test Step 2.
NOT OK - The speed sensor has failed.Repair: The speed sensor has failed. Replace the sensor. Adjust the speed sensor properly when the sensor is being installed. See Testing and Adjusting, "Speed Sensor - Adjust". Verify that the new sensor corrects the problem.STOPTest Step 2. CHECK THE RETURN CIRCUIT.
The machine harness remains disconnected from the sensor.
Turn the key start switch to the OFF position.
At the machine harness connector for the sensor, measure the resistance between contact 1 (451-BR(Brown)) and frame ground. Expected Result:The resistance should measure 20 ohms or less.Results:
OK - The resistance measures 20 ohms or less. The return circuit is correct. Proceed to Test Step 3.
NOT OK - The resistance does not measure 20 ohms or less.Repair: The return circuit (451-BR(Brown)) in the machine harness has excessive resistance (open). Repair or replace the machine harness.STOPTest Step 3. CHECK THE SIGNAL CIRCUIT FOR AN OPEN IN THE MACHINE HARNESS.
At the machine harness connector for the speed sensor, place a jumper between the two contacts.
Disconnect the machine harness connectors J1 and J2 from the ECM.
At the machine harness connectors J1 and J2, measure the resistance from J1-2 to J1-3. Expected Result:There should be less than 5.0 ohms resistance. Results:
OK - There is less than 5.0 ohms resistance. The signal circuit in the machine harness is correct. Proceed to Test Step 4.
NOT OK - There is not less than 5.0 ohms resistance.Repair: The signal circuit (450-YL(Yellow)) is open in the machine harness. Repair or replace the machine harness.STOPTest Step 4. CHECK THE SIGNAL CIRCUIT FOR