3500B Industrial Engines Caterpillar

The engine speed control is used to provide a throttle signal via the throttle position sensor to the engine control. The output for rated speed is a pulse width modulated signal. The signal varies with the position of the speed adjust potentiometer. The output signal is expressed as a percentage between 0 and 100 percent for the speed adjust potentiometer.

The ECM calculates the desired engine speed. The desired engine speed is produced by the signal from the rated speed setting. The rated speed signal is valid when the duty cycle is in the range of 5 to 95 percent. If the rated speed signal is invalid, the engine will be set to the low idle.

Some applications may choose not to use the speed control. Some applications may use a load sharing unit. The unit is configured to provide the engine control with a rated speed signal. Some of these 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	g00696374

Test Step 1. Check the Electrical Connectors and the Wiring.

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

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

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

Results:

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

• Not OK - Repair the wiring and connectors or replace the wiring or the connectors. Ensure that all of the seals are properly connected. Verify that the repair eliminates the problem.STOP

Test Step 2. Check the Voltage at the Speed Control.

1. Connect the red probe of the digital multimeter to the + Battery terminal of the Speed Control. Connect the black probe of the digital multimeter to the − Battery terminal of the Speed Control.

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

3. Turn the Battery switch for the ECM to the ON position.

Expected Result:

The digital multimeter should read 24 ± 5 VDC.

Results:

• OK - The digital multimeter reads 24 ± 5 VDC. The voltage supply to the Speed Control is correct. Proceed to test step 3.

• Not OK - The digital multimeter did not read 24 ± 5 VDC. There is a problem with the supply voltage to the Speed Control.

  Repair: Check the voltage at the battery. If the voltage at the battery is correct repair the connectors and/or the wiring between the speed control and the battery. If the battery voltage is incorrect refer to Testing and Adjusting, "Electrical System".

  STOP

Test Step 3. Check the Throttle Position on the ET.

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

2. Connect the ET to the service tool connector.

3. Turn the Battery switch for the ECM to the ON position.

4. Observe the position of the throttle on the ET.

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

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

Expected Result:

The throttle position on the ET should read 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.STOP

• Not OK - The throttle position on the ET does not respond correctly to adjustments in the speed adjust potentiometer. Proceed to test step 4.

Test Step 4. Check the Signal from the Speed Control.

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

2. Remove the wire from the S terminal at the Speed Control.

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 the S terminal of the Speed Control. Place the other probe on the − Battery terminal of the Speed Control.

5. Turn the Battery switch for the ECM to the ON position.

6. Monitor the output of the percent duty cycle from the Speed Control on the multimeter. Turn the potentiometer from the low setting to the high setting.

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

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

8. Reconnect all wires.

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 Speed Control is supplying the correct signal. Proceed to test step 5.

• 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 5. Check the Signal from the Speed Control at the ECM Input.

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

2. Install a Breakout T at ECM connectors P1 and P2.

3. Turn the Battery switch for the ECM to the ON position.

4. Measure the PWM signal at the ECM connector between P2-24 and P1-29.

5. Monitor the output of the percent duty cycle from the Speed Control on the multimeter. Monitor the percent throttle position on the ET. Turn the speed adjust potentiometer from the low setting to the high setting.

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. The percent throttle position should be between 0 and 100 percent for the above settings of the speed adjust potentiometer.

Results:

• OK - The duty cycle is correct. The ECM is not processing the signal correctly.

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

  STOP

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

  Repair: There is a problem in the wiring between P2-24 and the S terminal of the Speed Control. Repair the connectors or wiring and/or replace the connectors or wiring.

  STOP

• Not OK - Throttle Position - 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 Troubleshooting, "Replacing the ECM".

  STOP