C7.1 Industrial Engine and Generator Set Caterpillar

This procedure covers the following codes:

Also, use this procedure if the digital throttle position sensor is suspected of incorrect operation.

If a fault occurs with the primary throttle, and a secondary throttle is installed, the engine will use the secondary throttle until the fault is repaired.

If a fault occurs with the secondary throttle, the engine will use the primary throttle until the fault is repaired.

If a functional throttle is not available, the following conditions will occur:

• The engine will default to the limp home speed.

• If the engine speed is higher than the limp home speed, the engine will decelerate to the limp home speed.

• If the engine speed is lower than the limp home speed, the engine speed will remain at the current speed.

• The engine will remain at this speed while the diagnostic code remains active.

• All inputs from the faulty throttle are ignored by the ECM until the fault is repaired.

• All inputs from the repaired throttle will be ignored by the ECM until the keyswitch has been cycled.

Digital Throttle Position Sensor

The digital throttle position sensor is used to provide a digital throttle position signal to the ECM. The sensor output is a constant frequency signal with a pulse width that varies with the throttle position. This output signal is referred to as either a duty cycle or a pulse width modulated signal (PWM). This output signal is expressed as a percentage between 0 and 100 percent.

The digital throttle position sensor is most likely to be attached directly to the throttle assembly. The digital throttle position sensor requires no adjustment.

The duty cycle at low idle and the duty cycle at high idle can vary depending on the application. The percent of duty cycle is translated in the ECM into a throttle position of 3 to 100 percent.

The digital throttle position sensors are powered by +8 VDC from the ECM. The supply voltage is from the J1:4 to terminal "A" of the digital throttle position sensor connector.

If the application is using the ECM dedicated PTO functions, the digital throttle position sensor will be ignored while the engine is in PTO mode.

The ECM is in PTO mode if the PTO ON/OFF Switch is ON. This status can be checked with the electronic service tool. Refer to Troubleshooting, "PTO Switch Circuit - Test" for testing if the PTO is being used.

Illustration 1	g01927874
Typical schematic of the digital throttle position sensors

Illustration 2	g01980939
Typical example of the pin locations on connector P1 (1) Secondary sensor input (4) Sensor supply (+8 VDC) (5) Sensor return (66) Primary sensor input

Test Step 1. Inspect Electrical Connectors and Wiring

1. Inspect the OEM harness and the connectors on the harness. Thoroughly inspect the digital throttle position sensor connector. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

2. Perform a 45 N (10 lb) pull test on each wire in the ECM connector that is associated with the digital throttle position sensor:

   • P1:1

   • P1:4

   • P1:5

   • P1:66

3. Check the screw for the ECM connector for the correct torque of 6 N·m (53 lb in).

4. Check the harness for abrasion and pinch points from the digital throttle position sensor to the ECM.

Expected Result:

All connectors, pins, and sockets are correctly coupled and/or inserted and the harness is free of corrosion, of abrasion or of pinch points.

Results:

• OK - Proceed to Test Step 2.

• Not OK -

  Repair: Perform the following repair:

  Repair the connectors or the harness and/or replace the connectors or the harness. Ensure that all of the seals are correctly in place and ensure that the connectors are correctly coupled.

  Use the electronic service tool in order to clear all logged diagnostic codes and then verify that the repair eliminates the fault.

  STOP

Test Step 2. Check for Active Diagnostic Codes

1. Connect the electronic service tool to the diagnostic connector.

2. Turn the keyswitch to the ON position.

3. Monitor the active diagnostic code screen on the electronic service tool. Check and record active diagnostic codes.

   Note: When the ECM automatically calibrates new duty cycle values for the low idle throttle position and the high idle throttle position, the ECM assumes the initial lower position for the duty cycle at low idle and the initial upper position for the duty cycle at high idle. The initial lower position and the initial upper position can be obtained by accessing the following screens on the electronic service tool:

   • "Service"

   • "Throttle Configuration"

   • For throttle position sensor 1, select "Throttle# 1". For throttle position sensor 2 , select "Throttle# 2".

   As a result, you may notice that the throttle position status reaches 100 percent well before the throttle pedal is fully depressed. This situation is normal. After some cycling of the throttle to the high idle position, the ECM will adjust the calibration automatically, if the high idle stop position is within the duty cycle range, and the low idle is in the duty cycle range. During normal operation, more movement of the throttle can be required for the throttle position status to increase above 3 percent. The status may reach the 100 percent value prior to the limit of the high idle position. This is done in order to ensure that the throttle reaches these two critical points for engine operation.

Expected Result:

Result 1 The electronic service tool displays the following active diagnostic codes or recently logged diagnostic codes:

• 91-3 Accelerator Pedal Position 1 : Voltage Above Normal

• 91-4 Accelerator Pedal Position 1 : Voltage Below Normal

• 29-3 Accelerator Pedal Position 2 : Voltage Above Normal

• 29-4 Accelerator Pedal Position 2 : Voltage Below Normal

• 91-8 Accelerator Pedal Position 1 : Abnormal Frequency, Pulse Width or Period

• 29-8 Accelerator Pedal Position 1 : Abnormal Frequency, Pulse Width or Period

Result 2 The electronic service tool displays the following active diagnostic codes or recently logged diagnostic codes:

• 678-3 ECU 8 Volts DC Supply : Voltage Above Normal

• 678-4 ECU 8 Volts DC Supply : Voltage Below Normal

Result 3 There are no active diagnostic codes that are related to the digital throttle position sensor circuit at this time. A fault is suspected with operation of the sensor circuit.

Results:

• Result 1 - Proceed to Test Step 3.

• Result 2 - Proceed to Test Step 4.

• Result 3 - Proceed to Test Step 3.

Test Step 3. Check the Duty Cycle of the Digital Throttle Position Sensor

1. Access the following screens on the electronic service tool in order to check the upper and the lower diagnostic limit of the throttle position sensors:

   • "Service"

   • "Throttle Configuration"

   • For a 91-X code, select "Throttle# 1". For a 29-X code, select "Throttle# 2".

2. Make a note of the lower diagnostic limit and the upper diagnostic limit.

3. Verify that the keyswitch is in the ON position.

4. Access the following screens on the electronic service tool in order to monitor the duty cycle of the throttle position:

   • "Status"

   • "Throttles"

5. Monitor the duty cycle of the throttle at the "low idle" position and the "high idle" position.

Expected Result:

The duty cycle is above the lower diagnostic limit with the throttle in the low idle position. The duty cycle is below the upper diagnostic limit with the throttle in the high idle position.

Results:

• OK - The digital throttle position sensor is operating correctly. The fault may be intermittent.

  Repair: Perform a "Wiggle Test" by using the electronic service tool in order to identify intermittent faults. Refer to Troubleshooting, "Electrical Connectors - Inspect".

  STOP

• Not OK - The digital throttle position sensor circuit is not operating correctly. Proceed to Test Step 4.

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

1. Turn the keyswitch to the OFF position.

2. Install a breakout "T" with three terminals at the digital throttle position sensor connector.

3. Turn the keyswitch to the ON position.

4. Measure the voltage between terminal "A" (+8 VDC) and terminal "B" (digital throttle position sensor ground).

Results:

• The measured voltage is between 7.5 VDC and 8.5 VDC for the digital throttle position sensor - Proceed to Test Step 6.

• The sensor is not receiving the correct voltage - Proceed to Test Step 5.

Test Step 5. Disconnect the Power Supply Connections for the Digital Throttle Position Sensor at the ECM

1. Turn the keyswitch to the OFF position.

2. Disconnect connector P1. Thoroughly inspect the P1/J1 connector. Refer to Troubleshooting, "Electrical Connectors - Inspect" for more information.

3. Remove the P1:4 (+8 VDC). Remove the P1:5 (digital throttle position sensor ground) from connector P1.

4. Reconnect the P1 connector to the ECM.

5. Turn the keyswitch to the ON position.

6. Use the electronic service tool to check for active diagnostic codes.

Expected Result:

One of the following diagnostic codes is still active after the terminals for sensor power have been disconnected:

• 678-3 ECU 8 Volts DC Supply : Voltage Above Normal

• 678-4 ECU 8 Volts DC Supply : Voltage Below Normal

Results:

• OK -

  Repair: Perform the following repair:

  Check the battery voltage at pins 61, 63, 65, 67 and 69 (Battery ground) on the P1 connector. Check the battery voltage at pins 48, 52, 53, 55 and 57 (Battery+) on the J1 connector.. The measured voltage should be in one of the following ranges:

  • For 12 V systems, the voltage should be between 11.0 VDC and 13.5 VDC.

  • For 24 V systems, the voltage should be between 22.0 VDC and 27.0 VDC.
  If the voltage is correct, then perform the following procedure.

  1. Make sure that the latest flash file for the application is installed in the ECM. Refer to Troubleshooting, "Flash Programming".

  2. Contact the Technical Communicator at a Caterpillar Dealer.

     Note: This consultation can greatly reduce the repair time.

  3. If the Technical Communicator recommends the use of a test ECM, install a test ECM. Refer to Troubleshooting, "Replacing the ECM".

  4. Use the electronic service tool to recheck the system for active diagnostic codes.

  5. If the fault is resolved with the test ECM, reconnect the suspect ECM.

  6. If the fault returns with the suspect ECM, replace the ECM.

  7. Use the electronic service tool in order to clear all logged diagnostic codes and then verify that the repair eliminates the fault.

  STOP

• Not OK -

  Repair: Perform the following repair:

  There is a fault in the harness between the ECM and the digital throttle position sensor. While active diagnostic codes are being monitored, connect the removed wires one at a time in order to verify that the active diagnostic codes reappear. Replace pin P1:5 (digital throttle position sensor ground). Replace pin P1:4 (+8 V). This procedure is used to find the wire that is causing the fault. Repair the harness or replace the harness, as required.

  Use the electronic service tool in order to clear all logged diagnostic codes and then verify that the repair eliminates the fault.

  STOP

Test Step 6. Check the Duty Cycle of the Throttle Position Sensor at the Sensor

Note: Performing certain steps within this procedure requires the use of a multimeter that can measure a PWM duty cycle.

1. Access the following screens on the electronic service tool in order to check the upper and the lower diagnostic limit of the throttle position sensors:

   • "Service"

   • "Throttle Configuration"

   • For a 91-X code, select "Throttle# 1". For a 29-X code, select "Throttle# 2".

2. Make a note of the lower diagnostic limit and the upper diagnostic limit.

3. Turn the keyswitch to the OFF position.

4. Remove the signal wire for the digital throttle position sensor (terminal "C") from the connector. Refer to illustration 1.

5. Install a breakout "T" with three terminals at the digital throttle position sensor connector.

6. Connect the multimeter probes to terminal "C" (digital throttle position sensor signal) and terminal "B" (digital throttle position sensor ground) of the breakout T.

7. Turn the keyswitch to the ON position.

8. While the duty cycle is being monitored on the multimeter, operate the throttle through the full range of movement.

Expected Result:

The duty cycle is above the lower diagnostic limit with the throttle in the low idle position. The duty cycle is below the upper diagnostic limit with the throttle in the high idle position.

Results:

• OK - Reinsert the wire (terminal "C") into the harness connector of the digital throttle position sensor. The digital throttle position sensor is working correctly. Proceed to Test Step 7.

• Not OK - Leave the multimeter probe connected to the breakout "T". Insert the wire (terminal "C") into the machine harness connector. The throttle pedal assembly is faulty. Proceed to Test Step 8.

Test Step 7. Check the Duty Cycle of the Accelerator Pedal Position Sensor at the ECM

Note: Performing certain steps within this procedure requires the use of a multimeter that can measure a PWM duty cycle.

1. Access the following screens on the electronic service tool in order to check the upper and the lower diagnostic limit of the throttle position sensors:

   • "Service"

   • "Throttle Configuration"

   • For a 91-X code, select "Throttle# 1". For a 29-X code, select "Throttle# 2".

2. Make a note of the lower diagnostic limit and the upper diagnostic limit.

3. Turn the keyswitch to the OFF position.

4. Disconnect the P1 connector. Remove pin P1:66 for digital throttle position sensor 1 or pin P1:1 for digital throttle position sensor 2.

5. Connect the multimeter probes between the removed wire and pin P1:5 (digital throttle position sensor ground).

6. Reconnect the P1 connector to the ECM.

7. Turn the keyswitch to the ON position.

8. Use the multimeter in order to display the duty cycle output of the digital throttle position sensor. While the duty cycle output of the digital throttle position sensor is being monitored on the multimeter, move the throttle from the low idle position to the high idle position. Record the results.

9. Turn the keyswitch to the OFF position.

10. Remove the P1 connector from the ECM.

11. Install the pin for the digital throttle position sensor that was previously removed .

12. Connect the P1 connector to the ECM.

Expected Result:

The duty cycle is above the lower diagnostic limit with the throttle in the low idle position. The duty cycle is below the upper diagnostic limit with the throttle in the high idle position.

Results:

• OK - A good signal from the digital throttle position sensor is reaching the ECM.

  Repair: Perform the following repair:

  Check the battery voltage at pins 61, 63, 65, 67 and 69 (Battery ground) on the P1 connector. Check the battery voltage at pins 48, 52, 53, 55 and 57 (Battery+) on the J1 connector.. The measured voltage should be in one of the following ranges:

  • For 12 V systems, the voltage should be between 11.0 VDC and 13.5 VDC.

  • For 24 V systems, the voltage should be between 22.0 VDC and 27.0 VDC.
  If the voltage is correct, then perform the following procedure.

  1. Make sure that the latest flash file for the application is installed in the ECM. Refer to Troubleshooting, "Flash Programming".

  2. Contact the Technical Communicator at a Caterpillar Dealer.

     Note: This consultation can greatly reduce the repair time.

  3. If the Technical Communicator recommends the use of a test ECM, install a test ECM. Refer to Troubleshooting, "Replacing the ECM".

  4. Use the electronic service tool to recheck the system for active diagnostic codes.

  5. If the fault is eliminated with the test ECM, reconnect the suspect ECM.

  6. If the fault returns with the suspect ECM, replace the ECM.

  7. Use the electronic service tool in order to clear all logged diagnostic codes and then verify that the repair eliminates the fault.

  STOP

• Not OK - There is a fault with signal wire in the harness. Proceed to Test Step 9.

Test Step 8. Remove the Digital Throttle Position Sensor from the Throttle Pedal Assembly

Illustration 3	g01185326
Typical throttle assembly (1) Sensor mounting face (2) Sensor drive key (3) Mounting screw holes

Illustration 4	g01185327
Throttle block assembly (1) Mounting screw holes (2) Sensor housing (3) Sensor drive slot

Illustration 5	g01185328
Throttle block assembly (1) Mounting screw holes (2) Sensor drive slot (3) Sensor mounting face

1. Verify that the keyswitch is in the OFF position.

2. Note the sensor orientation in the throttle assembly and the sensor connector for the harness routing prior to sensor removal. Remove the digital throttle position sensor from the throttle assembly. Thoroughly inspect the connector and the harness for signs of abrasion.

3. Connect a multimeter that can measure a PWM duty cycle to terminal "C" of the breakout "T".

4. Turn the keyswitch to the ON position.

5. Display the duty cycle output of the digital throttle position sensor while the sensor slot is released. Use a screwdriver to advance the sensor slot to the maximum position. Refer to Illustration 5.

Expected Result:

When the sensor is removed from the throttle assembly and the sensor slot is released, the duty cycle is 10 percent or less. When the sensor slot is moved to the maximum position, the duty cycle increases to 90 percent or more.

Results:

• OK - The digital throttle position sensor is working correctly. Refer to the OEM dealer for correct replacement of the throttle assembly.

  STOP

• Not OK - The digital throttle position sensor is faulty. Check the throttle assembly in order to ensure that the throttle assembly is not damaging the sensor. If the throttle assembly is damaging the sensor, refer to the OEM dealer for correct replacement of the throttle assembly. If the throttle assembly appears OK, replace the digital throttle position sensor.

  STOP

Test Step 9. Route the Supply Bypass Wires to the Digital Throttle Position Sensor

1. Turn the keyswitch to the OFF position.

2. For digital throttle position sensor 1, temporarily remove the signal wire from P1:66. For digital throttle position sensor 2, temporarily remove the signal wire fromP1:1.

3. Remove terminal "C" (digital throttle position sensor signal) from the digital throttle position sensor connector.

4. Route the new wiring from the ECM to the digital throttle position sensor.

5. Access the following screens on the electronic service tool in order to check the upper and the lower diagnostic limit of the throttle position sensors:

   • "Service"

   • "Throttle Configuration"

   • For a 91-X code, select "Throttle# 1". For a 29-X code, select "Throttle# 2".

6. Make a note of the lower diagnostic limit and the upper diagnostic limit.

7. Turn the keyswitch to the ON position.

8. Check the duty cycle of the digital throttle position sensor on the electronic service tool while the digital throttle is being moved over the full range.

Expected Result:

The duty cycle is above the lower diagnostic limit with the throttle in the low idle position. The duty cycle is below the upper diagnostic limit with the throttle in the high idle position.

Results:

• OK -

  Repair: Perform the following repair:

  The wiring from the ECM to the digital throttle position sensor appears faulty. Permanently install new wiring.

  Use the electronic service tool in order to clear all logged diagnostic codes and then verify that the repair eliminates the fault.

  STOP

• Not OK - Double check the wiring, the P1/J1 connectors, and the digital throttle position sensor connector. If a fault still exists, repeat the test procedure from Test Step 1.

  STOP