3500B Industrial 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 speed. When the engine reaches the set point, an overspeed shutdown is initiated. This action will test the shutoff system. The Overspeed Verify Switch allows you to verify proper operation of the system.

Illustration 1	g00751568

Test Step 1. Check the Electrical Connectors and the Wiring.

1. Turn the Battery switch for the ECM to the OFF position.

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

3. Thoroughly inspect the ECM connectors J1/P1. Inspect all of the other connectors. Refer to Troubleshooting, "Inspecting Electrical Connectors" 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:

All connectors, pins, and sockets are completely coupled and/or inserted, and the harness and wiring should be free of corrosion, abrasion or pinch points.

Results:

• OK - The wiring and connectors are okay. Proceed to Test Step 2.

• Not OK - Repair the wiring and connectors or replace the wiring or the connectors. Ensure that all of the seals are properly connected. Verify that the repair eliminates the problem.STOP

Test Step 2. Check the Circuit of the Overspeed Verify Switch on the ET.

1. Install the ET to the service tool connector.

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

3. Turn the Battery switch for the ECM to the ON position.

4. Operate the Overspeed Verify Switch. Observe the status for the Overspeed Verify Switch on the ET.

Expected Result:

The status of the Overspeed Verify Switch should read "ON" with the Overspeed Verify Switch in the Closed position. The status of the intermediate speed should read "OFF" when the Overspeed Verify Switch is in the Open position.

Results:

• OK - The circuit of the Overspeed Verify Switch is operating normally.STOP

• Not OK - The circuit of the Overspeed Verify Switch is not operating normally. Proceed to Test Step 3.

Test Step 3. Check the Overspeed Verify Switch.

1. Turn the Battery switch for the ECM to the OFF position.

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 terminal 2 and terminal 3 on the Overspeed Verify Switch.

5. Measure the resistance between terminal 2 and terminal 3 on the Overspeed Verify Switch.

6. Turn the Overspeed Verify Switch to the ON position.

7. Measure the resistance between terminal 2 and terminal 3 on the Overspeed Verify Switch.

Expected Result:

The resistance should be greater than 20,000 Ohms with the Overspeed Verify Switch in the OFF position. The resistance should be 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. Turn the Battery switch for the ECM to the OFF position.

2. Disconnect the ECM connector J1/P1. Disconnect the wires from the Overspeed Verify Switch.

3. Measure the resistance between P1-29 and the engine ground.

4. Measure the resistance between P1-40 and the engine ground.

5. Measure the resistance between P1-29 and P1-40.

Expected Result:

The resistance should be greater than 20,000 Ohms.

Results:

• OK - The resistance is greater than 20,000 Ohms. 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. Short the wires from the Overspeed Verify Switch together at the Overspeed Verify Switch.

2. Measure the resistance between P1-29 and P1-40 at the ECM connector.

3. Replace all wires and remove all shorts.

Expected Result:

The resistance should be 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 Inputs from the Overspeed Verify Switch together at the ECM.

1. Turn the Battery switch for the ECM to the OFF position.

2. Disconnect the ECM connector J1/P1.

3. Install a Breakout T at the ECM connector J1/P1.

4. Remove wire P1-29 and P1-40 from the Breakout T on ECM connector P1.

5. Turn the Battery switch for the ECM to the ON position.

6. Observe the status of the Overspeed Verify Switch on the ET.

7. Short the wires from P1-29 and P1-40 together.

8. Observe the status of the Overspeed Verify Switch on the ET.

9. Turn the Battery switch to the OFF position.

10. Remove the Breakout T and reconnect ECM connector J1/P1.

Expected Result:

The status of the Overspeed Verify Switch changes to On when the wires are shorted together. The status of the Overspeed Verify Switch changes to Off when the wires are disconnected.

Results:

• OK - The status of the Overspeed Verify Switch changes to On when the wires are shorted together. The status of the Overspeed Verify Switch changes to Off when the wires are disconnected. The circuit for the Overspeed Verify Switch has an intermittent problem.

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

  STOP

• Not OK - The ECM is not reading the inputs from the Overspeed Verify Switch correctly.

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

  STOP