3512B Petroleum Engines with the ADEM 2 Electronic Control Module 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	g00894821
Typical example

Test Step 1. Check for Connector Damage.

1. Turn the engine control to the OFF position.

2. Thoroughly inspect the connectors J1/P1 and J2/P2 of the Electronic Control Module (ECM). Inspect all of the other connectors. Refer to the diagnostic functional test Troubleshooting, "Inspecting Electrical Connectors" for details.

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

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

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

6. 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 wiring and connectors are okay. Proceed to test step 3.

• Not OK - The wiring and/or connectors need repair.

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

  STOP

Test Step 2. Check the Status of the Overspeed Verify Switch on the Caterpillar Electronic Technician (ET).

1. Start the Cat ET.

2. Turn the engine control to the ON position.

3. Select the status screen on the Cat ET.

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

Expected Result:

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

Results:

• OK - The circuit for the overspeed verify switch is working correctly.

  Repair: The system is working correctly. Reset the system and check for any active diagnostic codes.

  STOP

• Not OK - The status screen is not changing in accordance with the switch position. Proceed to test step 3.

Test Step 3. Check the Overspeed Verify Switch.

1. Turn the engine control to the OFF position.

2. Remove the wire 150-OR from terminal 2 of the overspeed verify switch.

3. Connect a voltmeter between terminal 3 and terminal 2 of the overspeed verify switch.

4. Toggle the overspeed verify switch to the ON position. Toggle the overspeed verify switch to the OFF position. Measure the resistance between the terminals.

Expected Result:

The resistance should measure more than 20,000 Ohms when the overspeed verify switch is in the OFF position. The resistance should measure less than 10 Ohms when the overspeed verify switch is in the ON position.

Results:

• OK - The overspeed verify switch is working correctly. Proceed to test step 4.

• Not OK - The overspeed verify switch is not working correctly.

  Repair: Replace the overspeed verify switch. Reconnect all wires and connectors. Verify that the circuit is working properly.

  STOP

Test Step 4. Check the Voltage to the Overspeed Verify Switch.

1. Connect a voltmeter between the wire 150-OR from terminal 2 of the overspeed verify switch and engine ground.

2. Turn the engine control to the ON position.

3. Measure the voltage between the wire and engine ground.

4. Turn the engine control to the OFF position.

5. Reconnect all wires.

Expected Result:

The voltage should measure 24 ± 3 VDC.

Results:

• OK - The voltage measures 24 ± 3 VDC. Proceed to test step 5.

• Not OK - The voltage does not measure 24 ± 3 VDC.

  Repair: Check the wiring between terminal 2 of the overspeed verify switch and + Battery terminal.

  STOP

Test Step 5. Check for a Short in the Harness.

1. Turn the engine control to the OFF position.

2. Disconnect ECM connector J1/P1.

3. Ensure that the overspeed verify switch is in the OFF position.

4. Measure the resistance between the wire F706-PU at P1-13 and engine ground.

Expected Result:

The resistance should be 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 overspeed verify switch and the ECM. Proceed to test step 6.

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

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Reconnect all wires and connectors.

  STOP

Test Step 6. Check for an Open in the Harness.

1. Turn the engine control to the OFF position.

2. Disconnect ECM connector J1/P1.

3. Use a suitable piece of wire to short the wire at terminal 3 of the overspeed verify switch to engine ground.

4. Measure the resistance between the wire F706-PU at P1-13 and engine ground.

5. Reconnect all wires and connectors.

Expected Result:

The resistance should measure less than 10 Ohms.

Results:

• OK - The resistance measures less than 10 Ohms. Proceed to test step 7.

• Not OK - The resistance measures more than 10 Ohms. There is an open circuit in the harness between the overspeed verify switch and the ECM.

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

  STOP

Test Step 7. Short the Inputs of the Overspeed Verify Switch to the ECM.

1. Turn the engine control to the OFF position.

2. Disconnect ECM connector J1/P1.

3. Remove wire F706-PU at ECM connector P1-13. Install a wire jumper into the socket for P1-13.

4. Short the wire jumper to the + Battery terminal.

5. Turn the engine control to the ON position.

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

7. Turn the engine control to the OFF position.

8. Remove the wire short from P1-13.

9. Turn the engine control to the ON position.

10. Observe the status of the Overspeed Verify Switch on the Cat ET.

11. Turn the engine control to the OFF position.

12. Remove the wire jumper and reconnect all wires and connectors.

Expected Result:

The status of the overspeed verify switch should read "ON" with the short in place.

The status of the overspeed verify switch should read "OFF" when the wire is removed.

Results:

• OK - The ECM is responding correctly to changes to the inputs to the ECM. The harness is faulty.

  Repair: There may be an intermittent problem. Perform the diagnostic functional test Troubleshooting, "Inspecting Electrical Connectors" if the problem is intermittent.

  STOP

• Not OK - The ECM is not reading the correct status of the inputs to the ECM.

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

  STOP