3406E and 3456 Generator Set 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. This feature is disabled if "Overspeed Shutdown" is programmed to OFF.

Illustration 1	g01068183

Test Step 1. INSPECT ELECTRICAL CONNECTORS AND WIRING

1. Verify that there are no tripped circuit breakers.

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

3. Turn the engine control switch (ECS) to the OFF/RESET position.

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

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

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

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

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

Expected Result:

The connectors and wiring are free of damage, of abrasion, and of pinch points. The wiring harness and wiring connectors are completely inserted and the wiring harness and wiring connectors are free of corrosion.

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. Verify that the repair has eliminated the problem.

  STOP

Test Step 2. CHECK THE SWITCH STATUS ON CAT ET.

1. Connect the Caterpillar Electronic Technician (ET) to the service tool connector.

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

3. Select the status screen on Cat ET.

4. Toggle the overspeed verify switch to the OFF position. 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 changes 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. Turn the ECS to the OFF/RESET position.

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

3. Connect the terminals for the overspeed verify switch by using a jumper wire with socket terminals at each end.

4. Turn the ECS to the STOP position.

5. Observe the status screen on Cat ET.

6. Turn the ECS to the OFF/RESET position.

7. Disconnect the shorted terminals that were created for the overspeed verify switch.

8. Turn the ECS to the STOP position.

9. Observe the status screen on Cat ET.

10. Reconnect all wires.

Expected Result:

The status of the overspeed verify switch reads "ON" when the switch inputs are shorted.

The status of the overspeed verify switch reads "OFF" when the switch inputs are not shorted.

Results:

• OK - The wiring harness and the ECM are working properly. The overspeed verify switch is not operating correctly.

  Repair: Replace the overspeed verify switch. Verify that the repair has eliminated the problem.

  STOP

• Not OK - There is a problem in the wiring harness and/or the ECM. Proceed to Test Step 4.

Test Step 4. CHECK FOR A SHORT CIRCUIT IN THE WIRING HARNESS.

1. Turn the ECS to the OFF/RESET position.

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

3. Measure the resistance between P1:15 (Overspeed verify switch) and the engine ground.

4. Measure the resistance between P1:29 (Digital return) and the engine ground.

5. Measure the resistance between P1:15 (Overspeed verify switch) and P1:29 (Digital return).

6. Measure the resistance between the engine ground and all the other pins in P1.

Expected Result:

The resistance is greater than 20,000 Ohms.

Results:

• OK - 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. Proceed to Test Step 5.

Test Step 5. ISOLATE THE SHORT CIRCUIT IN THE HARNESS

1. Disconnect J3/P3 machine connector and J1/P1 ECM connector.

2. Measure the resistance between P1:15 (Overspeed verify switch) and the engine ground.

3. Measure the resistance between P3:37 (Overspeed verify switch) and the engine ground.

4. Measure resistance between P1:29 (Digital return) and engine ground.

5. Measure the resistance between P3:09 (Digital return) and the engine ground.

Expected Result:

The resistance is greater than 20,000 Ohms.

Results:

• OK - This test indicates that there is not a short between the wiring harness and the ECM.

  Repair: Reconnect J3/P3.

  Proceed to test step 6.

• Not OK - The resistance is less than 20,000 Ohms. A short circuit to ground is indicated in one of the harness circuits.

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Verify that the problem has been eliminated.

  STOP

Test Step 6. CHECK THE RESISTANCE THROUGH THE HARNESS

1. Turn the ECS to the OFF/RESET position.

2. Disconnect ECM connector J1/P1.

3. Use a wire jumper to short wire from the overspeed verify switch to engine ground.

4. Measure the resistance between P1:15 (Overpseed verify switch) and P1:29 (Digital return).

5. Remove the wire jumper. Reconnect all wires and connectors.

Expected Result:

The resistance is less than 10 Ohms.

Results:

• OK - The ECM is reading the input for the overspeed verify switch correctly. Proceed to Test Step 8.

• Not OK - There is an open circuit or excessive resistance in the harness. Proceed to Test Step 7.

Test Step 7. CHECK THE WIRING HARNESS FOR AN OPEN CIRCUIT

1. Disconnect J1/P1 ECM connectors and J3/P3 (Customer connector). Also, disconnect the wires at the overspeed verify switch.

2. Measure the resistance between P1:15 (Overspeed verify switch) and P3:37 (Overspeed verify switch).

3. Measure the resistance between J3:37 (Overspeed verify switch) and wire N942-OR(Orange) on the overspeed verify switch.

4. Measure the resistance between P1:29 (Digital return) and P3:09 (Digital return).

5. Measure the resistance between J3:09 (Digital return) and wire 998-BR(Brown) at the overspeed verify switch.

6. Reconnect all wires and connectors.

Expected Result:

The resistance is less than 10 Ohms.

Results:

• OK - There is no open circuit in the wiring harness between the ECM and the overspeed verify switch. Proceed to Test Step 8.

• Not OK - There is an open circuit in one of the harness circuits.

  Repair: Repair the wire harness or replace the wire harness. Verify that the repair has eliminated the problem.

  STOP

Test Step 8. SHORT THE SWITCH INPUTS AT THE ECM

1. Disconnect J1/P1 ECM connector.

2. Remove P1:15 Overspeed verify switch andP:29 Digital return from the ECM connector P1.

3. Insert a wire jumper with socket terminals at each end into P1:15 and P1:29.

4. Reconnect all connectors and turn the ECS to the STOP position.

   Note: The digital return will no longer be connected to the other sensors and switches. Additional diagnostic codes will be generated from the ECM. Clear the codes after you complete this test.

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

6. Turn the ECS to the OFF/RESET position.

7. Disconnect J1/P1 ECM connectors and remove the wire jumper.

8. Reconnect all connectors.

9. Turn the ECS to the STOP position.

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

11. Turn the ECS to the OFF/RESET position and reconnect all wires and connectors.

Expected Result:

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

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

Results:

• OK - The ECM is properly reading the inputs at P1 but not at the overspeed verify switch.

  Repair: The harness is faulty. Repair the harness or replace the harness. Verify that the repair has eliminated the problem.

  STOP

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

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

  STOP