3512 and 3516 EUI Engines for 784B, 785B, 789B and 793B Off-Highway Trucks Caterpillar

The throttle position sensor provides a pulse width modulated signal (PWM) to the engine's Electronic Control Module (ECM). The signal varies with the throttle position. The pedal mounted throttle position sensor will produce a minimum duty cycle when the pedal is released. The pedal mounted throttle position sensor will produce a maximum duty cycle when the pedal is fully depressed.

The output of the throttle position sensor is a frequency with a pulse width that varies with the throttle position. The output signal is referred to as a duty cycle or as a PWM signal. The duty cycle of the output signal is between 22 and 88 percent. The ECM translates the duty cycle into a throttle position of 0 to 100 percent. The output frequency of the throttle position sensor is between 150 and 1000 Hz.

The throttle position sensor receives 12.7 ± 1.0 VDC from ECM connector P1-51 to pin A at the sensor connector. The sensor return line is pin B of the sensor connector. Pin B is connected to the digital return line P1-9 of the ECM. The sensor signal is pin C of the sensor connector. Pin C is connected to P1-10 of the ECM.

Illustration 1	g00934947

Test Step 1. Check for Connector Damage.

1. Turn the keyswitch to the OFF position.

2. Thoroughly inspect the ECM connector J1/P1 and the machine connector J2/P2. Inspect all of the other connectors. Refer to the diagnostic functional test Troubleshooting, "Inspecting Electrical Connectors" for details.

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

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

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

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

Expected Result:

The connectors and wiring are free of the following problems: damage, corrosion, abrasion and incorrect attachment.

Results:

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

• Not OK - The connectors and/or wiring need repair.

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

  Stop.

Test Step 2. Inspect the Throttle Assembly.

Inspect the throttle assembly for damaged components.

Expected Result:

The throttle assembly operates smoothly without excessive drag. The throttle assembly returns to the low idle position without assistance in less than one second.

Results:

• OK - The throttle assembly is operating correctly. Proceed to Test Step 3.

• Not OK - The throttle assembly is not operating correctly.

  Repair: Repair the throttle assembly or replace the throttle assembly. The throttle assembly should operate smoothly without excessive drag. The throttle assembly should return to the low idle position without assistance in less than one second.

  Stop.

Test Step 3. Check the Throttle Position with the Caterpillar Electronic Technician (ET).

1. Connect Cat ET to the cab service tool connector J31. Start Cat ET.

2. Turn the keyswitch to the ON position. The engine should be off.

3. Observe the throttle position reading on Cat ET.

4. Depress the throttle and release the throttle.

Expected Result:

The throttle position reads 0 percent when the throttle pedal is released. The throttle position increases to 100 percent when the throttle pedal is fully depressed.

Results:

• OK - The throttle position reads 0 percent when the throttle pedal is released. The throttle position increases to 100 percent when the throttle pedal is fully depressed. The throttle position sensor is okay.

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

  Stop.

• Not OK - The throttle position does not read 0 percent when the throttle pedal is released. The throttle position does not increase to 100 percent when the throttle pedal is fully depressed. The ECM is not receiving a correct signal from the sensor. There may be a problem in the harness. Proceed to Test Step 4.

Test Step 4. Check the Sensor Supply Voltage at the Throttle Position Sensor Connector.

1. Turn the keyswitch to the OFF position.

2. Disconnect the connector for the throttle position sensor J36/P36.

   Note: Disconnecting the sensor will generate an open circuit diagnostic code for any sensor that is disconnected. Troubleshoot the original diagnostic code. Reset the system. Delete the logged diagnostic codes when you are finished.

3. Turn the keyswitch to the ON position. The engine should be off.

4. Measure the sensor supply voltage at the connector between P36-A and P36-B.

Expected Result:

The voltage is 12.7 ± 1.0 VDC.

Results:

• OK - The voltage is 12.7 ± 1.0 VDC. The supply voltage is reaching the sensor. Proceed to Test Step 5.

• Not OK - The voltage is not 12.7 ± 1.0 VDC. The supply voltage is not reaching the sensor. Proceed to Test Step 8.

Test Step 5. Check the Signal Frequency and the Duty Cycle at the Throttle Position Sensor Connector.

1. Turn the keyswitch to the OFF position.

2. Remove wire A983-BU from P36-C at the sensor connector.

3. Turn the keyswitch to the ON position. The engine should be off.

4. Measure the frequency and the duty cycle between wire A983-BU and engine ground.

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

5. Depress the throttle and release the throttle.

6. Turn the keyswitch to the OFF position.

7. Reconnect all connectors and wires.

Expected Result:

The frequency is between 150 and 1000 Hz.

The duty cycle is between 10 and 22 percent when the throttle is released. The duty cycle is between 75 and 90 percent when the throttle is fully depressed.

Results:

• OK - A valid frequency and a valid duty cycle appear at the sensor connector. Proceed to Test Step 6.

• Not OK - A valid frequency and a valid duty cycle do not appear at the sensor connector.

  Repair: Replace the throttle position sensor. Verify that the new sensor is operating correctly.

  Stop.

Test Step 6. Check the Signal Frequency and the Duty Cycle at the ECM.

1. Remove wire A983-BU from P1-10 at the ECM connector P1.

2. Turn the keyswitch to the ON position. The engine should be off.

3. Measure the frequency and the duty cycle between wire A983-BU and the engine ground.

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

4. Depress the throttle and release the throttle.

5. Turn the keyswitch to the OFF position.

6. Reconnect all connectors and wires.

Expected Result:

The frequency is between 150 and 1000 Hz.

The duty cycle is between 10 and 22 percent when the throttle is released. The duty cycle is between 75 and 90 percent when the throttle is fully depressed.

Results:

• OK - A valid frequency and a valid duty cycle appear at the sensor connector. The correct frequency and duty cycle signal are present at the ECM. Proceed to Test Step 7.

• Not OK - A valid frequency and a valid duty cycle does not appear at the sensor connector.

  Repair: There is a problem in the wiring and/or connectors between the ECM and the throttle position sensor. Repair the connectors or wiring and/or replace the connectors or wiring.

  Stop.

Test Step 7. Check the Throttle Position with the Cat ET.

1. Turn the keyswitch to the ON position. The engine should be off.

2. Observe the throttle position on Cat ET.

3. Depress the throttle and release the throttle.

4. Turn the keyswitch to the OFF position.

Expected Result:

The throttle position reads 0 percent when the throttle pedal is released. The throttle position increases to 100 percent when the throttle pedal is fully depressed.

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

Results:

• OK - The throttle position reads 0 percent when the throttle pedal is released. The throttle position increases to 100 percent when the throttle pedal is fully depressed. The throttle position sensor is okay. There is an intermittent problem in the wiring and/or in the connectors between the ECM and the throttle position sensor.

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

  Stop.

• Not OK - The throttle position does not read 0 percent when the throttle pedal is released. The throttle position does not increase to 100 percent when the throttle pedal is fully depressed.

  Repair: The ECM is not reading the throttle position sensor signal correctly. Replace the ECM. Refer to the diagnostic procedure Troubleshooting, "Replacing the ECM.".

  Stop.

Test Step 8. Check the Sensor Supply Voltage at the ECM.

1. Remove wire A700-OR from P1-51 at the ECM connector P1.

2. Remove wire 998-BR from P1-9 at the ECM connector P1.

   Note: If you remove the sensor common from a sensor, an open circuit diagnostic code will be generated for that sensor. Troubleshoot the original code. Delete the logged diagnostic code when you are finished.

3. Turn the keyswitch to the ON position. The engine should be off.

4. Measure the sensor supply voltage between wire A700-OR and 998-BR at the ECM connector.

5. Turn the keyswitch to the OFF position.

6. Reconnect all connectors and wires.

Expected Result:

The voltage is 12.7 ± 1.0 VDC.

Results:

• OK - The voltage is 12.7 ± 1.0 VDC. There is an open circuit or excessive resistance in the harness between the ECM and the connector for the throttle position sensor.

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

  Stop.

• Not OK - The voltage is not 12.7 ± 1.0 VDC.

  Repair: Perform the diagnostic functional test Troubleshooting, "Electrical Power Supply".

  Stop.