MSS3s Machine Security System Caterpillar

The green LED of the status indicator informs the operator that the machine security system (MSS3s) ECM has recognized a valid key. The problem may be unrelated to the MSS. The source of the problem that is preventing an engine start can come from several sources. Ensure that all of the standard requirements for starting the machine have been met. A few examples of the requirements are listed here:

• Interlocks in the operator seat

• Hydraulic interlocks

• Gear of the machine

• Fuel level

This troubleshooting procedure will eliminate the MSS as a source of the starting problem.

Note: The wires that are identified in this procedure are not present on every machine. If the wire that is identified in this procedure is not present, proceed to the next Test Step.

Table 1

Troubleshooting Test Steps	Values	Results
1. CHECK THE DATA LINKS. A. Connect the Caterpillar Electronic Technician (Cat ET) service tool to the machine. B. Use a valid key to turn the keyswitch to the ON position. C. Use the Cat ET service tool to determine the status of the Cat data-link.	The data links are communicating with all the ECMs that are installed on the machine. Note: Some machines are equipped with only the MSS3s ECM.	Yes - The data links are communicating with all the ECMs that are installed on the machine. Proceed to Test Step 2. No - The data links are not communicating with all the ECMs that are installed on the machine. The Cat data-link has failed. Repair:Repair the data link circuits in the harness. STOP.
2. CHECK THE SYSTEM VOLTAGE AT THE MSS3s ECM. A. Measure the voltage between pin 1 and pin 3 of the MSS3s ECM.	The voltage is approximately system voltage.	Yes - The voltage is approximately system voltage. Proceed to Test Step 3. No - The voltage is not approximately system voltage. Repair: Check the battery and the associated wiring in the machine harness. STOP.
3. CHECK THE VOLTAGE FROM THE KEY SWITCH TO THE DRIVER (INPUT No. 1) OF THE ECM. A. Turn the keyswitch to the ON position. B. Measure the voltage between pin 24 and pin 29 if the wires are present. Record the reading.	Voltage should be present for all of the measurements. The voltage should be within 10% of the machine battery voltage.	Yes - The voltage is present and the voltage level is correct. The ECM is receiving voltage. Proceed to Test Step 4. No - The voltage was not correct, or no voltage was present. Repair: Check the harness for signs of damage. Repair or replace the harness. STOP.
4. CHECK THE VOLTAGE FROM THE KEY SWITCH TO THE DRIVER (INPUT No. 2) OF THE ECM. A. Turn and hold the keyswitch in the START position. B. Measure the voltage between pin 18 and pin 31 if the wires are present. Record the reading.	Voltage should be present for all measurements. The voltage should be within 10% of the battery voltage.	Yes - The voltage is present and the voltage level is correct. The ECM is receiving voltage. Proceed to Test Step 5. No - The voltage was not correct, or no voltage was present. Repair: Check the harness for signs of damage. Repair or replace the harness. STOP.
5. CHECK THE DRIVER (OUTPUT No. 1) VOLTAGE. Note: The output drivers of the MSS3s ECM are protected from excessive electrical current. Excessive electrical current is usually the result of a wire or a component that is shorted to ground. If the MSS3s ECM detects an excessive amount of electrical current, the MSS3s ECM will disable the output driver. A. Place the keyswitch in the ON position. With 7X-1710 Multimeter Probes check for voltage between pin 58 and pin 11 with the wires present. Do not disconnect the connector from the MSS3s ECM.	Voltage should be present. The voltage should be within 10% of the machine battery voltage.	Yes - The voltage is present and the voltage level is correct. Proceed to Test Step 6. No - The voltage was not correct. Proceed to Test Step 7.
6. CHECK THE DRIVER (OUTPUT No. 2) VOLTAGE. Note: The output drivers of the MSS3s ECM are protected from excessive electrical current. Excessive electrical current is usually the result of a wire or a component that is shorted to ground. If the MSS3s ECM detects an excessive amount of electrical current, the MSS3s ECM will disable the output driver. A. With the keyswitch in the START position, check for voltage between pin 52 and pin 5 with the wires present.	Voltage should be present. The voltage should be within 10% of the machine battery voltage.	Yes - The voltage is present and the voltage level is correct. The ECM is sending voltage to the driven components that will start the machine. Repair: The MSS has not caused the problem. Verify that the driven components are receiving voltage by measuring at the component. Consult the troubleshooting manual for the engine. STOP. No - The voltage was not correct. Proceed to Test Step 9.
7. CHECK FOR A FAILED COMPONENT ON OUTPUT DRIVER (No. 1). A. Turn the keyswitch and the disconnect switch to the OFF position. If the machine is not equipped with a disconnect switch, remove the negative wire from the battery. B. Disconnect the harness connector from the solenoid or the relay that is controlled by the output driver (No. 1). C. Turn the disconnect switch and the keyswitch to the ON position. If the machine is not equipped with a disconnect switch, reconnect the negative wire to the battery. D. Place the keyswitch in the ON position. With 7X-1710 Multimeter Probes check for voltage between pin 58 and pin 11 with the wires present. Do not disconnect the connector from the MSS3s ECM.	Voltage should be present. The voltage should be within 10% of the machine battery voltage.	Yes - The voltage is present and the voltage level is correct. The solenoid or the relay has failed. Repair: Replace the solenoid or relay. STOP. No - The voltage was not correct. Proceed to Test Step 8.
8. CHECK THE WIRES IN THE CIRCUIT OF OUTPUT DRIVER (No. 1). A. Turn the keyswitch and the disconnect switch to the OFF position. If the machine is not equipped with a disconnect switch, remove the negative wire from the battery. B. Verify that the harness connector remains disconnected from the relay that is controlled by the output driver (No. 1). C. Disconnect the 70-pin connector from the MSS3s ECM. D. Measure the resistance between pin 58 and frame ground, with the wires present. E. Measure the resistance between pin 11 and frame ground, with the wires present.	The resistance is greater than 5000 ohms.	Yes - The resistance is greater than 5000 ohms. The ECM may have failed, however, ECM failure is unlikely. Repair: Exit this procedure and perform this procedure again. If the cause of the failure is not found, contact the technical communicator at your Caterpillar dealer. Follow the steps in Troubleshooting, "ECM - Replace" if the ECM needs to be replaced. STOP. No - The resistance was not correct. Repair: There is a problem in the wiring. Check the harness for signs of damage. Repair or replace the harness. STOP.
9. CHECK FOR A FAILED COMPONENT ON OUTPUT DRIVER (No. 2). A. Turn the keyswitch and the disconnect switch to the OFF position. If the machine is not equipped with a disconnect switch, remove the negative wire from the battery. B. Disconnect the harness connector from the solenoid or the relay that is controlled by the output driver (No. 2). C. Turn the disconnect switch and the keyswitch to the ON position. If the machine is not equipped with a disconnect switch, reconnect the negative wire to the battery. D. Place the keyswitch in the START position. With 7X-1710 Multimeter Probes check for voltage between pin 52 and pin 5 with the wires present. Do not disconnect the connector from the MSS3s ECM.	Voltage should be present. The voltage should be within 10% of the machine battery voltage.	Yes - The voltage is present and the voltage level is correct. The solenoid or the relay has failed. Repair: Replace the solenoid or the relay. STOP. No - The voltage was not correct. Proceed to Test Step 10.
10. CHECK THE WIRES IN THE CIRCUIT OF THE OUTPUT DRIVER (No. 2). A. Turn the keyswitch and the disconnect switch to the OFF position. If the machine is not equipped with a disconnect switch, remove the negative wire from the battery. B. The harness connector remains disconnected from the solenoid or the relay that is controlled by the output driver (No. 2). C. Disconnect the 70-pin connector from the MSS3s ECM. D. Measure the resistance between pin 52 and frame ground, with the wires present. E. Measure the resistance between pin 5 and frame ground, with the wires present.	The resistance is greater than 5000 ohms.	Yes - The resistance is greater than 5000 ohms. The ECM may have failed, however, ECM failure is unlikely. Repair: Exit this procedure and perform this procedure again. If the cause of the failure is not found, contact the technical communicator at your Caterpillar dealer. Follow the steps in Troubleshooting, "ECM - Replace" if the ECM needs to be replaced. STOP. No - The resistance was not correct. Repair: There is a problem in the wiring. Check the wiring harness for signs of damage. Repair or replace the harness. STOP.