3508C, 3512C, and 3516C Locomotive Engines Caterpillar

The overspeed verify switch provides a way to check the system at 75 percent of the set point. The set point is 118 percent over the rated engine rpm. When the engine reaches the set point, the strategy for the overspeed is initiated. This action will test the shutoff system. The overspeed verify switch allows you to verify proper operation of the system.

Illustration 1	g01619419

Test Step 1. Check for Connector Damage.

1. Turn the engine control to the OFF position.

2. Turn the breaker at the battery to the OFF position.

3. Thoroughly inspect the ECM connectors J1/P1 and J2/P2. Inspect all of the other connectors. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

4. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the circuit.

5. Check the ECM connector (allen head screw) for the proper torque of 6.0 N·m (55 lb in).

6. Check the customer connector (allen head screw) for the proper torque of 2.25 ± 0.25 N·m (20 ± 2 lb in).

7. Check the harness and the wiring for abrasion and pinch points.

Expected Result:

The connectors and wiring should be free of the following problems: damage, corrosion, abrasion and incorrect attachment.

Results:

• OK - The connectors and wiring are okay. Proceed to test step 2.

• Not OK - The connectors and/or wiring are not okay.

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring.

  STOP

Test Step 2. Check the Switch status on ET.

1. Connect an Electronic Service Tool to the service tool connector.

2. Turn the breaker at the battery to the ON position.

3. Select the status screen on the ET.

4. Toggle the overspeed verify switch to the ON position. Toggle the overspeed verify switch to the OFF position. Toggle the overspeed verify switch to the ON position.

Expected Result:

The status of the overspeed verify switch changed in accordance with the switch position.

Results:

• OK - The status of the overspeed verify switch changed in accordance with the switch position.

  Repair: The overspeed verify switch and related circuitry is operating correctly.

  STOP

• Not OK - The status of the overspeed verify switch did not change in accordance with the switch position. Proceed to test step 3.

Test Step 3. Check the condition of the Overspeed Verify Switch.

Note: Record switch wiring before removing wire for correct reconnection.

1. Disconnect the main power.

2. Turn the overspeed verify switch to the OFF position.

3. Remove the wires from the terminals on the overspeed verify switch.

4. Connect a voltmeter between the terminals on the overspeed verify switch.

5. Measure the resistance between the terminals on the overspeed verify switch.

6. Turn the overspeed verify switch to the ON position.

7. Measure the resistance between the two terminals on the overspeed verify switch.

8. Reconnect all wires.

Expected Result:

The resistance is be greater than 20,000 Ohms with the Overspeed Verify Switch in the OFF position. The resistance is less than 10 Ohms with the overspeed verify switch in the ON position.

Results:

• OK - The resistance measurements are okay. The problem is not with the overspeed verify switch. Proceed to test step 4.

• Not OK - The resistance measurements are not okay. The Overspeed Verify Switch is not operating correctly.

  Repair: Replace the overspeed verify switch. Verify that the problem is no longer present.

  STOP

Test Step 4. Check for a Short Circuit in the Wiring Harness.

1. Disconnect the main power.

2. Disconnect the ECM connector J1/P1. Disconnect the wires from the overspeed verify switch.

3. Measure the resistance between P1-61 and the engine ground.

Expected Result:

The resistance is greater than 20,000 Ohms.

Results:

• OK - The resistance is greater than 20,000 Ohms. There are no shorts in the wiring harness between the switch and the ECM. Proceed to test step 5.

• Not OK - The resistance is less than 20,000 Ohms. There is a short in the harness between the switch and the ECM.

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Verify that the problem is no longer present.

  STOP

Test Step 5. Check the Wiring Harness for an Open Circuit.

1. Use a wire jumper to short wire F706-PU(Purple) from the overspeed verify switch to engine ground.

2. Measure resistance between P1-61 and engine ground.

3. Remove the wire short. Reconnect all wires and connectors.

Expected Result:

The resistance is less than 10 Ohms.

Results:

• OK - The resistance is less than 10 Ohms. Proceed to test step 6.

• Not OK - The resistance is greater than 10 Ohms. There is an open or excessive resistance in the harness.

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Verify that the problem is no longer present.

  STOP

Test Step 6. Short the Switch Input at the ECM.

1. Disconnect the main power.

2. Disconnect ECM connector J1/P1.

3. Remove the wire F706-PU(Purple) from socket P1-13 of ECM connector P1.

4. Insert a wire jumper with socket terminals at each end into P1-61.

5. Reconnect ECM connector J1/P1.

6. Connect the main power.

7. Observe the status of the overspeed verify switch on the Cat ET.

8. Short the wire jumper that is in P1-61 to engine ground.

9. Observe the status of the overspeed verify switch on the Cat ET.

10. Disconnect the main power. Remove the wire jumper and reconnect all wires and connectors.

Expected Result:

The status of the overspeed verify switch reads "OFF" when the wire is not shorted to ground.

The status of the overspeed verify switch reads "ON" with the wire short in place.

Results:

• OK - The ECM is reading the input for the overspeed verify switch correctly.

  Repair: The problem may be intermittent. If the problem is intermittent refer to Troubleshooting, "Electrical Connectors - Inspect".

  STOP

• Not OK - The ECM is not reading the input from the overspeed verify switch correctly.

  Repair: Replace the ECM. Refer to Troubleshooting, "ECM - Replace".

  STOP