3500B Engines for Caterpillar Built Power Modules with the ADEM 3 Electronic Control Module Caterpillar

Use this procedure to troubleshoot the electrical system if a problem is suspected with the speed control or if the diagnostic code in Table 1 is active or easily repeated.

The speed control provides a throttle signal and a droop signal to the engine's 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 applications may choose not to use the speed control. Some applications may use a load sharing module. The load sharing module is configured to provide the engine control with a rated speed signal. The signal has the same characteristics as the above defined signal. Some of these load sharing modules cannot provide a signal until the engine is running. In these cases, perform troubleshooting while the engine is running.

Illustration 1	g01166547
Typical circuit with engine control

Test Step 1. Inspect Electrical Connectors and Wiring

1. Place the engine control in the OFF/RESET mode.

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. Refer to the diagnostic functional test Troubleshooting, "Inspecting Electrical Connectors" for details.

6. Check the customer connector (allen head screw) for the proper torque. Refer to the diagnostic functional test Troubleshooting, "Inspecting Electrical Connectors" for details.

7. 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, and the harness and wiring are free of corrosion, of abrasion and of pinch points.

Results:

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

• Not OK - The connectors and/or wiring are not OK.

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

  STOP

Test Step 2. Check the Supply Voltage to the Speed Control

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

2. Place the engine control in the STOP mode.

3. Connect one probe of a voltmeter to the +Battery terminal of the speed control. Connect one probe of the voltmeter to the −Battery terminal of the speed control.

Expected Result:

The voltage is 24 ± 3 VDC.

Results:

• OK - The voltage is 24 ± 3 VDC. The voltage supply to the speed control is correct. Proceed to Test Step 3.

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

  Repair: Check wire 998-BK(Black) for continuity to the ECM connector P1-66. Check the wires for continuity to the "relay breaker". Check the breakers.

  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. Place the engine control in the STOP mode. Turn the battery disconnect switch to the ON position.

3. Observe the position of the throttle on the Caterpillar Electronic Technician (ET) as you turn the speed adjust potentiometer.

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

Expected Result:

The throttle position on Cat ET varies with the turning of the speed adjust potentiometer. The droop on Cat ET varies with the turning of the droop adjust potentiometer.

Results:

• RATED SPEED - The throttle position on Cat ET does not vary with the turning of the speed adjust potentiometer. Proceed to Test Step 4.

• DROOP SPEED - The droop on Cat ET does not vary with the turning of the droop adjust potentiometer. Proceed to Test Step 5.

• Unsure - The problem is not apparent. Proceed to Test Step 4.

Test Step 4. Check the Throttle Position

1. Place the engine control in the STOP mode. Turn the battery disconnect switch to the ON position.

2. Observe the position of the throttle on Cat ET.

3. Turn the speed adjust potentiometer to the lowest setting.

   • 60 Hz equals 1369 rpm.

   • 50 Hz equals 1141 rpm.

4. Start at the low idle position. Slowly turn the speed adjust potentiometer in the other direction. Monitor the position of the throttle on Cat ET.

Expected Result:

The throttle position on Cat ET reads 0 percent at the lowest setting and 0 to 100 percent as the speed adjust potentiometer is adjusted.

Results:

• OK - The speed control is operating correctly.

  Repair: The problem may be intermittent. If the problem is intermittent, perform the diagnostic functional test Troubleshooting, "Inspecting Electrical Connectors".

  STOP

• Not OK - The throttle position on Cat ET does not vary as the speed adjust potentiometer is adjusted. Proceed to Test Step 6.

Test Step 5. Check the Droop Signal on Cat ET

1. Place the engine control in the STOP mode. Turn the battery disconnect switch to the ON position.

2. Observe the droop on Cat ET.

3. Turn the droop adjust potentiometer in a counterclockwise direction.

4. Slowly turn the droop adjust potentiometer in a clockwise direction. Monitor the droop on Cat ET.

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

Expected Result:

The droop on Cat ET reads 0 percent at the lowest setting and 0 to 10 percent as the droop adjust potentiometer is adjusted.

Results:

• OK - The droop is operating correctly.

  Repair: The problem may be intermittent. If the problem is intermittent, perform the diagnostic functional test Troubleshooting, "Inspecting Electrical Connectors".

  STOP

• Not OK - The droop on Cat ET does not vary as the droop adjust potentiometer is adjusted. Proceed to Test Step 7.

Test Step 6. Check the Speed Control

1. Remove the wire from the S terminal at the speed control.

2. Set the multimeter to "VDC". Press the "Hz" button twice in order to display the "%" symbol.

3. Place one probe of the multimeter on the S terminal of the speed control. Place the other probe on the −Battery terminal of the speed control.

4. Monitor the output of the percent duty cycle from the speed control on the multimeter. Turn the speed adjust potentiometer from the low setting to the high setting.

   Note: The throttle position on Cat ET will not match the percent duty cycle on the multimeter.

Expected Result:

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

Results:

• OK - The speed control is supplying the correct duty cycle. Proceed to Test Step 8.

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

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

  STOP

Test Step 7. Check the Droop Signal at the Speed Control

1. Remove the wire from the D terminal of the speed control.

2. Set the multimeter to "VDC". Press the "Hz" button twice in order to display the "%" symbol.

3. Place one probe of the multimeter on the D terminal of the speed control. Place the other probe on the −Battery terminal of the speed control.

4. Monitor the output of the percent duty cycle from the speed control on the multimeter. Turn the droop adjust potentiometer from the low setting to the high setting.

   Note: The droop on Cat ET will not match the percent duty cycle on the multimeter.

Expected Result:

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

Results:

• OK - The speed control is providing the correct droop signal. Proceed to Test Step 9.

• Not OK - The problem appears to be in the speed control.

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

  STOP

Test Step 8. Check the Speed Signal at the ECM Input

1. Place the engine control in the STOP mode. Turn the battery disconnect switch to the ON position.

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

3. Measure the voltage between pins P1-10 and P2-66 on the ECM connectors.

4. Monitor the output of the percent duty cycle from the speed control on the multimeter. Monitor the percent throttle position on Cat ET. Turn the speed adjust potentiometer from the low setting to the high setting.

Expected Result:

The duty cycle is between 4 and 10 percent at the low setting and between 90 and 95 percent at the high setting. The percent throttle position is between 0 and 100 percent for the above settings of the speed adjust potentiometer.

Results:

• OK - The duty cycle is correct. Proceed to Test Step 5.

• Not OK - The duty cycle is not correct.

  Repair: There is a problem in the wiring between P1-10 and the S terminal of the speed control. Verify that the low idle switch is functioning properly.

  STOP

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

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

  STOP

Test Step 9. Check the Droop Signal at the ECM Input

1. Place the engine control in the STOP mode. Turn the battery disconnect switch to the ON position.

2. Measure the voltage between the pins P2-69 and P2-66 at the ECM connector.

3. Set the multimeter to "VDC". Press the "Hz" button twice in order to display the % symbol.

4. Monitor the output of the percent duty cycle of the droop signal at the speed control with the multimeter. Monitor the droop on Cat ET. 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.

Expected Result:

The duty cycle is between 1 and 15 percent at the clockwise setting and between 85 and 99 percent at the counterclockwise setting. The droop is between 0 and 100 percent for the above settings of the droop adjust potentiometer.

Results:

• OK - The duty cycle is correct.

  Repair:

  STOP

• Not OK - The duty cycle is not correct.

  Repair: There is a problem in the wiring between P2-69 and the D terminal of the speed control.

  STOP

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

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

  STOP