3512B Marine Auxiliary Engine Caterpillar

The loadshare unit provides the throttle signal and the droop signal to the Electronic Control Module (ECM). The output for rated speed is a pulse width modulated signal (PWM) at a constant frequency. The speed signal varies with the position of the speed adjust potentiometer. The output for droop is a PWM signal at a constant frequency. The droop signal varies with the position of the droop adjust potentiometer. The output signal is referred to as a duty cycle or as a PWM signal. The output signal is expressed as a percentage between 0 and 100 percent for the speed adjust and a percentage between 0 and 10 percent for the droop adjust.

The ECM calculates the desired engine rpm from the rated speed signal and the droop signal. The rated speed signal is valid when the duty cycle is in the range of 5 to 95 percent. If the ECM determines that the rated speed signal is invalid, the engine rpm will be set to the programmed low idle.

Note: Desired speed can be adjusted from 1369 to 1945 rpm for a 60 Hz system and from 1141 to 1621 rpm for a 50 Hz system.

The droop signal is valid when the duty cycle is in the range of 15 to 85 percent. If the ECM determines that the droop signal is invalid, the engine will run with NO droop which is referred to as Isochronous Mode. Some of these load sharing units can not provide a signal until the engine is running. In these cases, troubleshooting should be performed while the engine is running.

Illustration 1	g00814997

Note: The Engine Control Switch (ECS) is mounted within an instrument panel that is located on the right side of the engine. The ECS is locked into the AUTO position with a pin. The pin must be removed in order to perform this test. After performing this test, ensure that the ECS is placed in the AUTO position and that the locking pin has been reinstalled.

Test Step 1. Check for Connector Damage.

1. Turn the Engine Control Switch (ECS) to the OFF/RESET position.

2. Turn the battery disconnect switch to the OFF position.

3. Thoroughly inspect the ECM connectors J1/P1 and J2/P2. Inspect all of the other connectors. Refer to the diagnostic functional test 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, of abrasion or of pinch points.

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 Voltage to the Loadshare Unit.

1. Turn the battery disconnect switch to the ON position.

2. Connect one probe of a multimeter to + Battery terminal of the loadshare unit. Connect one probe of the multimeter to the - Battery terminal of the loadshare unit.

3. Measure the voltage from the + Battery terminal and the - Battery terminal of the speed control.

Expected Result:

The voltage should measure 24 ± 3 VDC.

Results:

• OK - The voltage measures 24 ± 3 VDC. The voltage supply to the loadshare unit is correct. Proceed to test step 3.

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

  Repair: There is a problem with the supply voltage to the loadshare unit. Check the supply voltage to the loadshare unit.

  Stop.

Test Step 3. Determine the Component that has Failed.

1. Determine if the problem is with the input for the throttle or the droop.

2. Turn the battery disconnect switch to the OFF position.

3. Connect the Caterpillar Electronic Technician (ET) to the engine ECM. Use the service tool connector J60/P60.

4. Turn the battery disconnect switch to the ON position.

5. Turn the ECS to the STOP position.

6. Observe the position of the throttle on the Cat ET as you turn the speed adjust potentiometer.

7. Observe the droop on the Cat ET as you turn the droop adjust potentiometer.

   Note: Do not overturn the droop adjust potentiometer in the clockwise direction. The signal will become erratic.

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

9. Turn the battery disconnect switch to the OFF position.

Expected Result:

The throttle position on the Cat ET should vary with the turning of the speed adjust potentiometer. The throttle position on the Cat ET should read 0 percent at the lowest setting and 0 to 100 percent as the speed adjust potentiometer is adjusted.

The droop on the Cat ET should vary with the turning of the droop adjust potentiometer. The droop on the Cat ET should read 0 percent at the lowest setting and 0 to 10 percent as the droop adjust potentiometer is adjusted.

Results:

• OK - Rated Speed, Droop Speed - The rated speed and the droop speed are correct. The throttle position on the Cat ET varies with the turning of the speed adjust potentiometer. The droop on the Cat ET varies with the turning of the droop adjust potentiometer.

  Repair: The circuit is working properly. If the problem is intermittent, perform the diagnostic functional test Troubleshooting, "Inspecting Electrical Connectors".

  Stop.

• Not OK - Rated Speed - The throttle position on the Cat ET does not vary with the turning of the Speed Adjust Potentiometer. Proceed to test step 4.

• Not OK - Droop Speed - The droop on the Cat ET does not vary with the turning of the droop adjust potentiometer. Proceed to test step 5.

Test Step 4. Check the Throttle Signal from the Loadshare Unit.

1. Remove the wire from terminal 19 at the loadshare unit.

2. Set the multimeter to "VDC". Press the "Hz" button twice so that the % symbol is displayed.

3. Place one probe of the multimeter on terminal 19 of the loadshare unit. Place the other probe on the - Battery terminal of the loadshare unit.

4. Turn the battery disconnect switch to the ON position.

5. Turn the ECS to the STOP position.

6. Monitor the output of the percent duty cycle from the loadshare unit on the multimeter. Turn the speed adjust potentiometer from the low setting to the high setting.

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

8. Turn the battery disconnect switch to the OFF position.

9. Reconnect the wire that was removed from the terminal 19 of the loadshare unit.

Expected Result:

The duty cycle should be between 4 and 10 percent at the low setting and between 90 and 95 percent at the high setting.

Results:

• OK - The loadshare unit is supplying the correct signal. Proceed to test step 6.

• Not OK - The duty cycle is not correct on the multimeter.

  Repair: Verify the proper operation of the speed adjust potentiometer. If the speed adjust potentiometer is operating correctly, temporarily install another loadshare unit. Verify that the problem is no longer present. Reinstall the old loadshare unit. If the problem returns, replace the loadshare unit.

  Stop.

Test Step 5. Check the Droop Signal from the Loadshare Unit.

1. Remove the wire from terminal 20 of the loadshare unit.

2. Set the multimeter to "VDC". Press the "Hz" button twice so that the % symbol is displayed.

3. Place one probe of the multimeter on terminal 20 of the loadshare unit. Place the other probe on the - Battery terminal of the loadshare unit.

4. Turn the battery disconnect switch to the ON position.

5. Turn the ECS to the STOP position.

6. Monitor the output of the percent duty cycle from the loadshare unit on the multimeter. Turn the droop adjust potentiometer from the low setting to the high setting.

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

8. Turn the battery disconnect switch to the OFF position.

9. Reconnect the wire that was removed from the terminal 20 of the loadshare unit.

Expected Result:

The duty cycle is between 15 and 85 percent. This range should be attainable.

Results:

• OK - The loadshare unit is providing the correct duty cycle for the Droop Signal. Proceed to test step 7.

• Not OK - The problem appears to be in the loadshare unit.

  Repair: Temporarily install another loadshare unit. Verify that the problem is no longer present. Reinstall the old loadshare unit. If the problem returns, replace the loadshare unit.

  Stop.

Test Step 6. Check the Throttle Input from the Loadshare Unit to the ECM.

1. Disconnect the primary ECM connector J2/P2. Remove wire 388-BU from P2-24.

2. Disconnect the secondary ECM connector J2/P2. Remove wire 388-BU from P2-24.

3. Set the multimeter to "VDC". Press the "Hz" button twice so that the % symbol is displayed.

4. Place one probe of the multimeter on wire 388-BU from the primary ECM. Place the other probe on the engine ground.

5. Turn the battery disconnect switch to the ON position.

6. Turn the ECS to the STOP position.

7. Monitor the output of the percent duty cycle from the loadshare unit on the multimeter. Turn the speed adjust potentiometer from the low setting to the high setting.

8. Place one probe of the multimeter on wire 388-BU from the secondary ECM. Place the other probe on the engine ground.

9. Monitor the output of the percent duty cycle from the loadshare unit on the multimeter. Turn the speed adjust potentiometer from the low setting to the high setting.

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

11. Turn the battery disconnect switch to the OFF position.

12. Reconnect all wires. Reconnect the ECM connectors.

Expected Result:

The duty cycle should be between 4 and 10 percent at the low setting and between 90 and 95 percent at the high setting.

Results:

• OK - Duty Cycle - The duty cycle is correct but the throttle position is not correct. The ECM is not processing the throttle signal correctly.

  Repair: The loadshare unit is providing the correct signal to the ECM. Replace the ECM. Refer to the diagnostic procedure Troubleshooting, "Replacing the ECM".

  Stop.

• Not OK - Duty Cycle - The duty cycle is not correct.

  Repair: There is a problem in the wiring between ECM connector P2-24 and terminal 19 of the speed control. Repair the connectors or wiring and/or replace the connectors or wiring.

  Stop.

Test Step 7. Check the Droop Signal from the Loadshare Unit to the ECM.

1. Disconnect the primary ECM connector J1/P1. Remove wire F721-GY from P1-19.

2. Disconnect the secondary ECM connector J1/P1. Remove wire F721-GY from P1-19.

3. Set the multimeter to "VDC". Press the "Hz" button twice so that the % symbol is displayed.

4. Place one probe of the multimeter on wire F721-GY from the primary ECM. Place the other probe on the engine ground.

5. Turn the battery disconnect switch to the ON position.

6. Turn the ECS to the STOP position.

7. Monitor the output of the percent duty cycle from the loadshare unit on the multimeter. Turn the droop adjust potentiometer from the low setting to the high setting.

   Note: Do not overturn the droop adjust potentiometer in the clockwise direction. The signal will become erratic.

8. Place one probe of the multimeter on wire F721-GY from the secondary ECM. Place the other probe on the engine ground.

9. Monitor the output of the percent duty cycle from the loadshare unit on the multimeter. Turn the droop adjust potentiometer from the low setting to the high setting.

   Note: Do not overturn the droop adjust potentiometer in the clockwise direction. The signal will become erratic.

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

11. Turn the battery disconnect switch to the OFF position.

12. Reconnect all wires. Reconnect the ECM connectors.

Expected Result:

The duty cycle should be between 1 and 15 percent at the clockwise setting and between 85 and 99 percent at the counterclockwise setting.

Results:

• OK - Duty Cycle - The duty cycle is correct but the droop is not correct. The ECM is not processing the droop signal correctly.

  Repair: The loadshare unit is providing the correct signal to the ECM. Replace the ECM. Refer to the diagnostic procedure Troubleshooting, "Replacing the ECM".

  Stop.

• Not OK - Duty Cycle - The duty cycle is not correct.

  Repair: There is a problem in the wiring between ECM connector P2-24 and terminal 20 of the loadshare unit. Repair the connectors or wiring and/or replace the connectors or wiring.

  Stop.