3500B Industrial Engines with the ADEM 3 Electronic Control Module Caterpillar

The overspeed verify switch provides a way to check the system at 75 percent of the overspeed setpoint. The overspeed setpoint is 118 percent over the rated engine speed. When the engine reaches the overspeed setpoint, 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	g01266344
Typical schematic

Illustration 2	g01266346
P1 connector for the Electronic Control Module (ECM) (P1-5) Digital return (P1-61) Overspeed verify switch (torque limiter)

Illustration 3	g01234146
Location of ECM connectors

Illustration 4	g01266349
Machine interface connector (Terminal 09) Digital return (Terminal 21) Overspeed verify switch (torque limiter)

Test Step 1. Inspect Electrical Connectors and Wiring

1. Turn the breaker for the ECM to the OFF position.

2. Thoroughly inspect the ECM connectors J1/P1. Inspect all of the other connectors. Refer to Troubleshooting, "Inspecting Electrical Connectors" for the proper procedure for inspecting system wiring.

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. Refer to Troubleshooting, "Inspecting Electrical Connectors" for details.

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

Expected Result:

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

Results:

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

• Not OK - There is a problem in the connectors and/or wiring.

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are completely coupled.Verify that the repair eliminates the problem.

  STOP

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

1. Connect Cat ET to the service tool connector.

2. Turn the breaker for the ECM to the ON position.

3. Turn the switch that provides power to the keyswitch input for the ECM to the ON position.

4. Operate the overspeed verify switch. Observe the status for the overspeed verify switch on Cat ET.

Expected Result:

The status of the overspeed verify switch reads "ON" with the overspeed verify switch in the ON position. The status of the overspeed verify switch reads "OFF" when the overspeed verify switch is in the OFF position.

Results:

• OK - The circuit for the overspeed verify switch is operating normally.

  Repair: If an intermittent condition is suspected, refer to Troubleshooting, "Inspecting Electrical Connectors".

  STOP

• Not OK - The circuit for the overspeed verify switch is not operating normally. Proceed to Test Step 3.

Test Step 3. Check the Overspeed Verify Switch

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

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

3. Measure the resistance between terminal 2 and terminal 3 on the overspeed verify switch.

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

5. Measure the resistance between terminal 2 and terminal 3 on the overspeed verify switch.

Expected Result:

The resistance measurement indicates an open circuit with the overspeed verify switch in the OFF position. The resistance measurement indicates a short circuit with the overspeed verify switch in the ON position.

Results:

• OK - The resistance measurements are OK. The problem is not with the overspeed verify switch. Proceed to Test Step 4.

• Not OK - The resistance measurements are not OK. 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 ECM connector J1/P1.

2. Measure the resistance between P1-05 and the engine ground.

3. Measure the resistance between P1-05 and every terminal on ECM connectors P1 and P2.

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

5. Measure the resistance between P1-61 and every terminal on ECM connectors P1 and P2.

Expected Result:

The resistance measurements for P1-61 indicate an open circuit. The resistance measurements for P1-05 indicate an open circuit except for terminals P1-23 and P1-28.

Note: Terminals P1-23 and P1-28 are connected to terminal P1-05 through the emergency stop switch.

Results:

• OK - The resistance measurements are OK. Proceed to Test Step 5.

• Not OK - The resistance measurements are not OK. 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. 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 P1-05 and P1-61 at the ECM connector.

3. Replace all wires and remove all shorts.

Expected Result:

The resistance measurement indicates a short circuit.

Results:

• OK - The resistance measurement indicates a short circuit. Proceed to Test Step 6.

• Not OK - The resistance measurement does not indicate a short circuit. There is an open or excessive resistance in the wires or connectors between the overspeed verify 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 6. Check the Operation of the ECM

1. Disconnect the ECM connector J1/P1.

2. Remove the wire for the overspeed verify switch from ECM connector P1-61. Install a wire jumper into the socket for P1-61. Ensure that the wire jumper is isolated from engine ground and any other wires.

3. Turn the breaker for the ECM to the ON position.

4. Turn the switch that provides power to the keyswitch input for the ECM to the ON position.

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

6. Fabricate a jumper wire.

   Connect the wire jumper in socket P1-61 to the digital return at socket P1-5.

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

8. Turn the switch that provides power to the keyswitch input for the ECM to the OFF position.

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

10. Replace all wires to the original configuration.

Expected Result:

The status of the overspeed verify switch is OFF when the wire jumper is isolated. The status of the overspeed verify switch changes to ON when the wire jumper is shorted to the digital return.

Results:

• OK - The status of the overspeed verify switch is correct. The ECM is operating correctly.

  Repair: Check the connectors for damage, looseness or corrosion. Refer to Troubleshooting, "Inspecting Electrical Connectors".

  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