3412E Petroleum Engine Caterpillar

Use this procedure to troubleshoot any suspect problems with the throttle position sensor. Also use this procedure to troubleshoot an active 91-08 Throttle Signal Abnormal.

If there is an active 91-13 Throttle Position calibration required, refer to Troubleshooting, "Throttle Position Sensor - Calibrate".

The Throttle Position Sensor (TPS) utilizes the lever movement by the operator to send an electrical signal to the Electronic Control Module (ECM). The signal from the TPS and the signal from the speed/timing sensors are processed by the ECM in order to control the engine speed.

Note: The direct fuel control replaces the throttle position sensor when an external governor is used. An electrical converter converts the 0 to 200 mA current from the governor into a pulse width modulated signal that can be used by the ECM. The use of the direct fuel control will disable the engine governor control and engine speed control that is provided by the ECM software.

The sensor that is installed depends on the engine's configuration.

Illustration 1	g01123466
Electronic throttle position sensor

Illustration 2	g01122049
Throttle position sensor with a lever

Illustration 3	g01122050
Throttle position sensor with a knob

The sensor creates a signal that is pulse width modulated. The duty cycle varies with the throttle position. The signal has a low duty cycle when the throttle is at low idle. The signal has a high duty cycle when the throttle is at high idle. The Electronic Control Module (ECM) processes the signal in order to control the engine speed. Refer to Illustration 4.

Illustration 4	g01139809
Duty cycle versus throttle position

The signal from the throttle position sensor has a specific frequency. The frequency of the signal must be between 150 Hz and 1050 Hz or the ECM will activate a 91-08 diagnostic code.

Illustration 5	g01137894
Schematic for throttle position sensor

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The connection of any electrical equipment and the disconnection of any electrical equipment may cause an explosion hazard which may result in injury or death. Do not connect any electrical equipment or disconnect any electrical equipment in an explosive atmosphere.

Test Step 1. Identify the Type of Speed Control System for the Engine

Determine if a throttle position sensor or direct fuel control is being used to control engine speed.

Expected Result:

A throttle position sensor is used to control engine speed.

Results:

• OK - A throttle position sensor is used to control engine speed. Proceed to Test Step 2.

• Not OK - Direct fuel control is used to control engine speed. Proceed to Test Step 8.

Test Step 2. Check the Programmable Parameters

1. Connect the Caterpillar Electronic Technician (ET) to the service tool connector.

2. Turn the keyswitch to the ON position.

3. Check the "Direct Fuel Mode" parameter for the programmed value.

Expected Result:

The "Direct Fuel Mode" is programmed to "OFF".

Results:

• OK - The "Direct Fuel Mode" is programmed to "OFF". The engine is configured for the use of a throttle position sensor. Proceed to Test Step 3.

• Not OK - The "Direct Fuel Mode" is programmed to "ON", but the engine is configured for the use of a throttle position sensor.

  Repair: Program the "Direct Fuel Mode" parameter to "OFF". Verify that the repair eliminates the problem.

  STOP

Test Step 3. Inspect the Connectors and the Wiring for the Throttle Position Sensor

1. Turn the keyswitch to the OFF position.

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Illustration 6	g01137932
Top view (1) J2/P2s ECM connector (2) P3 Customer connector

2. Thoroughly inspect connectors (1) and (2). Also inspect the connector for the throttle position sensor. Refer to Troubleshooting, "Electrical Connectors - Inspect".

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Illustration 7	g01137937
P2 terminal that is associated with the throttle position sensor (P2-24) Throttle position

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Illustration 8	g01137941
J3 connector and P3 connector (Terminal 10) Throttle position

3. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the throttle position sensor.

4. Check the allen head screw on each ECM connector and the customer connector for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.

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

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 wiring and the connectors are OK. Proceed to Test Step 4.

• Not OK - There is a problem with the wiring and/or the connectors.

  Repair: Repair the wiring and/or the connectors. Replace parts, if necessary. Ensure that all of the seals are properly connected. Verify that the repair eliminates the problem.

  STOP

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

1. Disconnect the P35 connector.

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

3. Measure the voltage between terminals P35-A and P35-B.

Expected Result:

The supply voltage is at least 11 VDC for a 12 volt system. The supply voltage is at least 22 VDC for a 24 volt system.

Results:

• OK - The supply voltage is at least 11 VDC for a 12 volt system. The supply voltage is at least 22 VDC for a 24 volt system. The supply voltage is reaching the sensor. Proceed to Test Step 5.

• Not OK - The supply voltage is incorrect.

  Repair: The configuration of the wiring between the +Battery and the throttle position sensor depends on the engine's configuration. The problem could be in the wiring or in a connector. There may be a problem with the battery.Perform the necessary repairs. Verify that the problem is resolved.

  STOP

Test Step 5. Check the Signal Wire for a Short Circuit

1. Turn the keyswitch to the OFF position.

2. Disconnect the P2 ECM connector.

Note: Be sure to wiggle the harnesses during the following measurements. Be sure to wiggle each harness near each connector.

3. Measure the resistance between terminal P1-24 and all of the other terminals in the P1 ECM connector.

Expected Result:

Each resistance measurement indicates an open circuit.

Results:

• OK - Each resistance measurement indicates an open circuit. Proceed to Test Step 6.

• Not OK - At least one resistance measurement does not indicate an open circuit. There is a short circuit in the signal wire for the throttle position sensor.

  Repair: The problem could be in the wiring or in a connector. Repair the wiring and/or the connector, when possible. Replace parts, if necessary. Verify that the problem is resolved.

  STOP

Test Step 6. Check the Signal Wire for an Open Circuit

Note: Be sure to wiggle the harnesses during the following measurement. Be sure to wiggle each harness near each connector.

Measure the resistance between terminal P2-24 and terminal P35-C.

Expected Result:

The resistance measurement is less than ten Ohms.

Results:

• OK - The resistance measurement is less than ten Ohms. The wire is OK. Connect the P35 connector. Proceed to Test Step 7.

• Not OK - The resistance measurement is greater than ten Ohms. There is excessive resistance in the signal wire.

  Repair: The problem could be in the wiring or in a connector. Repair the wiring and/or the connector, when possible. Replace parts, if necessary. Verify that the problem is resolved.

  STOP

Test Step 7. Check the Frequency of the Throttle Position Signal at the ECM

1. Turn the keyswitch to the OFF position.

2. Ensure that Cat ET is connected to the service tool connector. Refer to Troubleshooting, "Electronic Service Tools".

3. Connect a 40-pin breakout between the P2 ECM connector and the J2 ECM connector.

4. Connect a multimeter between terminals 24 on the breakout t and the engine ground stud.

5. Turn the keyswitch to the ON position.

6. Measure the frequency of the throttle position signal. Slowly move the throttle from low idle to high idle and back to low idle while you measure the frequency of the signal.

7. Observe Cat ET for active diagnostic codes. Slowly move the throttle from the low idle position to the high idle position. Look for a 91-08 diagnostic code while you move the throttle.

8. Turn the keyswitch to the OFF position.

Expected Result:

The frequency of the signal remains between 150 Hz and 1050 Hz as you move the throttle. A 91-08 diagnostic code is not activated.

Results:

• OK - The frequency of the signal remains between 150 Hz and 1050 Hz as you move the throttle. A 91-08 diagnostic code is not activated.

  Repair: Perform the following procedure:

  1. Remove the 40-pin breakout.

  2. Connect the J2/P2 ECM connectors.

  3. Turn the keyswitch to the ON position.

  4. Operate the throttle throughout the entire range.

     If the problem does not recur, the problem is resolved. The original problem was probably caused by a poor electrical connection. Return the engine to service.

  STOP

• Not OK - The frequency of the signal is incorrect. A 91-08 diagnostic code is activated.

  Repair: Perform the following procedure:

  1. Replace the throttle position sensor. Check for a 91-08 diagnostic code again.

     If the diagnostic code does not recur, the problem is resolved. Return the engine to service.

     If the diagnostic code recurs, replace the ECM. Refer to Troubleshooting, "Replacing the ECM". Verify that the problem is resolved.

  STOP

Test Step 8. Check Programmable Parameters

1. Connect Cat ET to the data link connector.

2. Turn the keyswitch to the ON position.

3. Make sure that the "Direct Fuel Mode" parameter is programmed to "On".

Expected Result:

The "Direct Fuel Mode" is programmed to "On".

Results:

• OK - The "Direct Fuel Mode" is programmed to "On". Proceed to Test Step 9.

• Not OK -

  Repair: Program the "Direct Fuel Mode" parameter to "On".Verify that the repair eliminates the problem.

  STOP

Test Step 9. Inspect the Connectors and the Wiring for the Direct Fuel Control Mode

Illustration 9	g01138096
Schematic for direct fuel control mode

1. Turn the keyswitch to the OFF position.

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Illustration 10	g01137932
Top view (1) J2/P2 ECM connector (2) P3 Customer connector

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Illustration 11	g01138046
Signal converter for the direct fuel control mode

2. Thoroughly inspect connectors (1) and (2). Inspect the connections on the signal converter. Refer to Troubleshooting, "Electrical Connectors - Inspect".

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Illustration 12	g01137937
P2 terminal that is associated with the direct fuel control mode (P2-24) Throttle position

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Illustration 13	g01137941
J3 and P3 terminal that is associated with the direct fuel control mode (10) Throttle position

3. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the direct fuel control mode.

4. Check the allen head screw on each ECM connector and the customer connector for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.

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

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 wiring and the connectors are OK. Proceed to Test Step 10.

• Not OK - There is a problem with the wiring and/or the connectors.

  Repair: Repair the wiring and/or the connectors. Replace parts, if necessary. Ensure that all of the seals are properly connected. Verify that the repair eliminates the problem.

  STOP

Test Step 10. Check the Voltage Supply to the Signal Converter

1. Turn the keyswitch to the ON position.

2. Measure the voltage across terminal 4 (+Battery) and terminal 6 (-Battery) of the converter.

Expected Result:

The voltage is between 22 VDC and 27 VDC.

Results:

• OK - The converter is receiving the proper supply voltage. Proceed to Test Step 11.

• Not OK - The supply voltage is incorrect.

  Repair: The configuration of the wiring between the +Battery and the signal converter depends on the engine's configuration. The problem could be in the wiring or in a connector. There may be a problem with the battery.Perform the necessary repairs. Verify that the problem is resolved.

  STOP

Test Step 11. Check the Current Input to the Signal Converter

1. Measure the current (mA) across terminal 1 and terminal 3 of the signal converter.

2. Move the throttle from the low idle position to the high idle position.

Expected Result:

The current is 0 mA at low idle and the current is 200 mA at high idle.

Results:

• OK - The signal converter is receiving the proper input. Proceed to Test Step 12.

• Not OK - The signal converter is not receiving the proper input.

  Repair: Make sure that the governor is turned on. Check the wiring between the signal converter and the governor. Repair the wiring.

  STOP

Test Step 12. Measure the Duty Cycle at the Signal Converter

1. Turn the keyswitch to the ON position.

2. Measure the duty cycle between terminal 12 (throttle signal) and engine ground.

3. Move the throttle from the low idle position to the high idle position.

Expected Result:

The duty cycle is between 5.0 percent and 10.0 percent when the throttle is at low idle. The duty cycle is 90.0 percent to 95.0 percent when the throttle is at high idle.

Results:

• OK - The duty cycle is within the specified range. Proceed to Test Step 13.

• Not OK - The duty cycle is not within the specified range.

  Repair: Perform this test step again in order to verify the results. Replace the converter. Verify that the repair eliminates the problem.

  STOP

Test Step 13. Measure the Duty Cycle at the ECM

1. Turn the keyswitch to the ON position.

2. Measure the duty cycle between P2-24 throttle signal and engine ground.

3. Move the throttle from the low idle position to the high idle position. Record the measurements.

4. Turn the keyswitch to the OFF position.

Expected Result:

The duty cycle is between 5.0 percent and 10.0 percent when the throttle is at low idle. The duty cycle is 90.0 percent to 95.0 percent when the throttle is at high idle.

Results:

• OK - The duty cycle is within the specified range.

  Repair: There may be a problem with the ECM. Temporarily install a test ECM. If the problem is corrected, install the suspect ECM. If the problem returns, permanently install the new ECM. Refer to Troubleshooting, "Replacing the ECM" before replacing the ECM.

  STOP

• Not OK - The duty cycle is not within the specified range. Proceed to Test Step 14.

Test Step 14. Check for Short Circuits in the Wiring Harness

1. Disconnect the J2/P2 ECM connectors.

2. Measure the resistance between P2-24 throttle signal and the engine ground.

3. Measure the resistance between P2-24 throttle signal and each of the terminals in the P2 ECM connector.

Expected Result:

All measurements indicate an open circuit.

Results:

• OK - All measurements indicate an open circuit. There are no short circuits in the wiring harness. Proceed to Test Step 15.

• Not OK - An excessive resistance was measured for at least one of the measurements.

  Repair: There is a short circuit in the wiring harness. The problem could be in the wiring or in a connector. Repair the wiring and/or the connector, when possible. Replace parts, if necessary. Verify that the problem is resolved.

  STOP

Test Step 15. Check for Open Circuits in the Wiring Harness

1. Disconnect the J2/P2 ECM connectors and remove terminal 12 of the converter.

2. Measure the resistance between terminal 12 of the converter and P2-24 throttle signal.

Expected Result:

The resistance is less than five ohms.

Results:

• OK - The measurement was less than five ohms.

  Repair: The direct fuel control seems to be working properly at this time. There may be an intermittent problem in the harness. Refer to Troubleshooting, "Electrical Connectors - Inspect " for information that is related to troubleshooting an intermittent electrical problem.If a problem with the installation of the signal converter is suspected, refer to the appropriate Special Instruction for information that is related to the installation of the converter.

  STOP

• Not OK - There is a open circuit in the wiring harness.

  Repair: The problem could be in the wiring or in a connector. Repair the wiring and/or the connector, when possible. Replace parts, if necessary. Verify that the problem is resolved.

  STOP