C11 and C15 Engines for Caterpillar Built Machines Caterpillar

Use this procedure to troubleshoot any suspect problems with the circuit for the throttle position sensor. This procedure covers the following diagnostic codes:

• 91-08 Throttle Position Signal abnormal

• 774-08 Sec Throttle Position Sensor signal abnormal

The throttle position sensor provides the throttle signal to the Electronic Control Module (ECM). The throttle position sensor is mounted to a pedal assembly that allows the operator to control the speed of the engine. The geometry of the pedal assembly controls both the travel of the sensor and the range of the output signal. The throttle position sensor cannot be adjusted.

The output from the throttle position sensor is a PWM signal that varies with the position of the throttle pedal. The throttle position sensor produces a minimum duty cycle in the released position and a maximum duty cycle in the fully depressed position. When the pedal is released, the ECM translates the sensor's output signal to a throttle position of 0 percent. When the pedal is fully depressed, the ECM translates the output signal to a throttle position of 100 percent.

The throttle position sensor is powered by 8.0 ± 0.4 VDC that is provided by the ECM. A digital return for the sensor is also provided by the ECM.

The ECM uses an automatic calibration function that allows the ECM to minimize the deadband of the sensor. The automatic calibration function assumes a range of PWM duty cycle at powerup. If the duty cycle of the sensor exceeds this initial range, the automatic calibration function adjusts the limits of the duty cycle in order to adjust for the new range.

Illustration 1	g01260415
Schematic for throttle position sensor

Test Step 1. Inspect the Electrical Connectors and the Wiring

1. Remove the electrical power from the ECM.
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   Illustration 2	g01141049
   J1/P1 ECM connector

2. Thoroughly inspect the J1/P1 ECM connector and the connector for the throttle position sensor. Inspect the machine connector for damage or corrosion. Refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect" for details.
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   Illustration 3	g01260430
   P1 ECM connector (P1-4) 8 VDC supply (P1-5) Digital return (P1-66) Throttle position (P1-68) Secondary throttle position

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   Illustration 4	g01265123
   Terminals on the machine connector (Terminal 8) 8 VDC supply (Terminal 9) Digital return (C15) (Terminal 10) Throttle (Terminal 11) Secondary throttle C15) (Terminal 15) Digital return (C11) (Terminal 38) Secondary throttle C11)

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   Illustration 5	g01159881
   J403/P403 for the throttle position sensor (A) 8 V supply (B) Digital return (C) Throttle position

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

4. Check the allen head screw from each ECM connector for the proper torque. Refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect" for the correct torque value.

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

Expected Result:

All of the 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 harness and connectors appear to be OK. Proceed to Test Step 2.

• Not OK - The connectors and/or wiring are not OK.

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are completely coupled.

  Verify that the repair eliminates the problem.

  STOP

Test Step 2. Inspect the Throttle Pedal Assembly

1. Inspect the throttle pedal assembly for components that are loose, bent, missing, or worn.

2. Slowly depress the pedal and release the pedal.

Expected Result:

The throttle pedal assembly operates smoothly without excessive drag. The pedal springs back smoothly to the low idle position without assistance.

Results:

• OK - The throttle pedal assembly functions properly. Proceed to Test Step 3.

• Not OK - The throttle pedal assembly is in poor repair.

  Repair: Repair the throttle pedal assembly or replace the throttle pedal assembly, as required.

  STOP

Test Step 3. Check the Status for "Throttle Position"

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

2. Restore the electrical power to the ECM.

3. Observe the status for "Throttle Position" on Cat ET while you operate the throttle pedal through the entire range of travel.

Expected Result:

The status is zero percent when the throttle pedal is released. The status progressively increases to 100 percent when the throttle pedal is fully depressed.

Results:

• OK - The throttle position sensor is working properly.

  Repair: There may be an intermittent electrical problem with the harness or the connectors. Refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect".

  STOP

• Not OK - The throttle position that is displayed on Cat ET does not correspond to the movement of the throttle pedal. Proceed to Test Step 4.

Test Step 4. Check the Supply Voltage at the Sensor

1. Disconnect the connector for the throttle position sensor.

2. Restore the electrical power to the ECM.

3. Measure the voltage across terminal A (8 V supply) and terminal B (digital return) on the harness side of the connector.

4. Remove the electrical power from the ECM.

Expected Result:

The supply voltage measures 8.0 ± 0.4 VDC at the sensor connector.

Results:

• OK - The correct voltage is measured at the sensor connector. The sensor is receiving the correct supply voltage. Proceed to Test Step 5.

• Not OK - The voltage is not correct at the sensor connector. The sensor is not receiving the correct supply voltage. Proceed to Test Step 7.

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

1. Install a 7X-6370 Adapter Cable As (3-PIN BREAKOUT) at the connector for the throttle position sensor.

2. Remove the signal wire from terminal C of the connector for the throttle position sensor. Remove the wire from the harness side of the connector.

3. Restore the electrical power to the ECM.

4. Measure the frequency and the duty cycle between terminal B (digital return) and terminal C (throttle position) at the 7X-6370 Adapter Cable As (3-PIN BREAKOUT) while you operate the throttle pedal.

5. Remove the electrical power from the ECM.

6. Remove the breakout harness. Restore the wires to the original configuration.

Expected Result:

The frequency is between 150 and 1000 Hz. The duty cycle is between 7 and 95 percent.

Results:

• OK - The frequency and the duty cycle are within specifications for the entire range of the pedal. The sensor is producing a valid signal. Proceed to Test Step 6.

• Not OK - The frequency and the duty cycle are not within specifications.

  Repair: The sensor is not producing a valid signal. Replace the throttle position sensor. Verify that the repair eliminates the problem.

  STOP

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

1. Install a 208-0059 Adapter Cable As (70-PIN BREAKOUT) between the J1 and the P1 ECM connectors.

2. Restore the electrical power to the ECM.

3. Measure the frequency between terminals P1-66 (throttle position) and P1-5 (digital return) on the breakout harness while you operate the throttle pedal.

4. Measure the duty cycle of the sensor. Measure the duty cycle between terminals P1-66 (throttle position) and P1-5 (digital return) on the breakout harness while you operate the throttle pedal.

5. Remove the electrical power from the ECM.

Expected Result:

The frequency is between 150 and 1000 Hz. The duty cycle is between 7 percent and 95 percent.

Results:

• OK - The frequency and the duty cycle are within specifications for the entire range of the pedal.

  Repair: A valid signal appears at the ECM, but the ECM is not reading the signal properly. Replace the ECM. Refer to electronic troubleshooting Troubleshooting, "Replacing the ECM" for complete instructions. Verify that the repair eliminates the problem.

  STOP

• Not OK - The frequency and the duty cycle are not within specifications.

  Repair: There is not a valid signal at the ECM connector. Repair the signal wire in the harness. Verify that the repair eliminates the problem.

  STOP

Test Step 7. Check the Supply Voltage at the ECM

1. Disconnect the J1/P1 ECM connector.

2. Remove the wires from terminals P1-4 (8 VDC supply) and P1-5 (digital return). Install jumper wires into the terminal locations for the digital return wire and the supply wire.

3. Reconnect the J1/P1 ECM connector.

4. Restore the electrical power to the ECM.

5. Measure the voltage between the wire jumpers in terminals P1-4 (8 VDC supply) and P1-5 (digital return).

6. Remove the electrical power from the ECM.

Expected Result:

The supply voltage measures 8.0 ± 0.4 VDC at the ECM.

Results:

• OK - The correct voltage is measured at the ECM.

  Repair: There is an open circuit or excessive resistance in the harness between the ECM and the sensor. Repair the circuit. Verify that the repair eliminates the problem.

  STOP

• Not OK - The voltage is not correct at the ECM.

  Repair: The ECM does not appear to be producing the correct supply voltage. Replace the ECM. Refer to electronic troubleshooting Troubleshooting, "Replacing the ECM" for complete instructions. Verify that the repair eliminates the problem.

  STOP