C9 Marine Auxiliary and Marine Generator Set Engines Caterpillar

The rotary position sensor provides a throttle 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 throttle signal varies with the position of the rotary position sensor. The output signal is referred to as a duty cycle or as a Pulse Width Modulated signal (PWM). The output signal is expressed as a percentage between 0 and 100 percent for the speed adjust.

The ECM calculates the desired engine rpm from the rated speed 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.

Some applications may choose not to use the rotary position sensor. 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 can not provide a signal until the engine is running. In these cases, troubleshooting should be performed while the engine is running.

Illustration 1	g01173277
Schematic

Illustration 2	g00766798
Percent of throttle position versus PWM input

Illustration 3	g01173295
P1 ECM connector (P1-66) Primary speed signal (P1-44) Droop-Isoch switch (P1-68) Secondary speed signal

Test Step 1. Check for Connector Damage.

1. Turn the keyswitch to the OFF position.

2. Thoroughly inspect the J61/P61 customer connector, the J1/P1 ECM connector, the J2/P2 ECM connector and any related connectors. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

3. Perform a 45 N (10 lb) pull test on each of the wires in the connectors.

4. Check each connectors (allen head screw) for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

5. Check the harness and wiring for abrasions and for pinch points from the battery to the ECM.

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 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 Supply Voltage to the Rotary Position Sensor

1. Connect one probe of a voltmeter to the +Battery terminal of the rotary position sensor. Connect one probe of the voltmeter to the −Battery terminal of the rotary position sensor.

2. Turn the keyswitch to the ON position.

3. Measure the battery voltage at the rotary position sensor.

Expected Result:

The supply voltage is between 11.0 VDC and 13.5 VDC for a 12 Volt system and the supply voltage is between 22.0 VDC and 27.0 VDC for a 24 Volt system.

Results:

• OK - The supply voltage is reaching the rotary position sensor. Proceed to Test Step 5.

• Not OK - The supply voltage is not reaching the rotary position sensor. Proceed to Test Step 3.

Test Step 3. Measure the No-Load Battery Voltage

1. Measure the no-load battery voltage at the battery posts.

   Note: Load test the batteries by using the 4C-4911 Battery Load Tester. Refer to Special Instruction, SEHS9249, "Use of the 4C-4911 Battery Load Tester" and Special Instruction, SEHS7633, "Battery Test Procedure" for further assistance.

Expected Result:

The no-load voltage is at least 11.0 VDC for a 12 Volt system and the no-load voltage is at least 22.0 VDC for a 24 Volt system. The batteries pass the load test.

Results:

• OK - The voltage is in the range at the battery posts.

  Repair: Repair the wiring between the battery and the rotary position sensor.

  STOP

• Not OK - The voltage is out of the range at the battery posts.

  Repair: The battery voltage is out of the range.

  1. Replace the batteries.

  2. Repeat the battery test.

  3. Verify that the problem is eliminated.

  4. Clear all logged diagnostic codes.

  STOP

Test Step 4. Check the Duty Cycle at the Customer Connector

1. Turn the keyswitch to the OFF position.

2. Remove the signal wires from the customer connector P61:10 and P61:4.

3. Turn the keyswitch to the ON position.

4. Measure the duty cycle between P61:10 and the −Battery. Measure the duty cycle between P61:4 and the −Battery.

5. Move the throttle from low idle to high idle and monitor the duty cycle output of the throttle position sensor on the multimeter.

6. Turn the keyswitch to the OFF position.

7. Reconnect the signal wires to the customer connector.

Expected Result:

The duty cycle is between 5 percent and 10 percent when the throttle is at low idle. The duty cycle is between 90 percent to 95 percent when the throttle is at high idle.

Results:

• OK - A valid signal appears at the customer connector. Your application is equipped with an engine control. Proceed to Test Step 5 .

• OK - A valid signal appears at the customer connector. Your application is not equipped with an engine control. Proceed to Test Step 6.

• Not OK - A valid signal is not present at the customer connector.

  Repair: Perform the following diagnostic procedure.

  1. Verify that a valid signal is present at the rotary position sensor. If a valid signal is present at the rotary position sensor, repair the corresponding signal wire between the customer connectors J61:10 or J61:4and the rotary position sensor.

  2. If a valid signal is not present at the speed control, replace the rotary position sensor. Verify that the repair fixes the problem.

  STOP

Test Step 5. Check the Duty Cycle at the Engine Control Connector (if applicable)

1. Turn the keyswitch to the OFF position.

2. Remove the wire M971-BR(Brown) from the engine control connector.

3. Turn the keyswitch to the ON position.

4. Fabricate a jumper wire. Measure the duty cycle between wire M971-BR(Brown) and the −Battery.

5. Move the throttle from low idle to high idle and monitor the duty cycle output of the throttle position sensor on the multimeter.

6. Turn the keyswitch to the OFF position.

7. Reconnect the wire M971-BR(Brown) to the engine control connector.

Expected Result:

The duty cycle is between 5 percent and 10 percent when the throttle is at low idle. The duty cycle is between 90 percent to 95 percent when the throttle is at high idle.

Results:

• OK - A valid signal appears at the engine control connector. Proceed to Test Step 6.

• Not OK - A valid signal is not present on the M971-BR(Brown) at the engine control connector.

  Repair: Replace the wire M971-BR(Brown) between the connectors.

  STOP

Test Step 6. Check the Duty Cycle at the ECM

1. Remove the wire M971-BR(Brown) from ECM connector P1:66. Remove the wire M974-YL(Yellow) from ECM connector P1:68.

2. Turn the keyswitch to the ON position.

3. Measure the duty cycle between wire M971-BR(Brown) and the −Battery. Measure the duty cycle between wire M974-YL(Yellow) and the −Battery.

4. Move the throttle from low idle to high idle and monitor the duty cycle output of the throttle position sensor on the multimeter.

Expected Result:

The duty cycle is between 5 percent and 10 percent when the throttle is at low idle. The duty cycle is between 90 percent to 95 percent when the throttle is at high idle.

Results:

• OK - The duty cycle is in the range.

  Repair:

  1. Turn the keyswitch to the OFF position.

  2. Reconnect the original wiring.

  3. Turn the keyswitch to the ON position.

  4. Check for the active diagnostic code 91-08.
  If the diagnostic code 91-08 is present, replace the ECM. Refer to the diagnostic procedure Troubleshooting, "Replacing the ECM".

  STOP

• Not OK - The signal is not present at the ECM.

  Repair: Replace the wires between the ECM connector and the customer connector.

  STOP