C27 and C32 Industrial and Petroleum Engines Caterpillar

The throttle position sensor eliminates the mechanical throttle and governor linkages. 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

Refer to Illustration 4. Pulse Width Modulation (PWM) is used to provide the throttle position to the ECM. 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.

Illustration 4	g01122143
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	g01213002

Schematic for the throttle position sensor

Test Step 1. Inspect the Electrical Connectors and the Wiring

1. Remove electrical power from the ECM.
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   Illustration 6	g01167488
   Engine view (typical example) (1) J1/P1 ECM connectors

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   Illustration 7	g01146383
   Engine view (typical example) (2) J61 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 8	g01213008
   P1 terminal that is associated with the throttle position sensor (P1-66) Throttle position signal

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   Illustration 9	g01213033
   Terminal location at the P61 customer connector that is associated with the throttle position sensor (10) Throttle position signal

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 for the proper torque. Also, check the allen head screw on 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 keyswitch and the engine ground.

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 2.

• 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 in good repair. Verify that the repair eliminates the problem.

  STOP

Test Step 2. Check for Supply Voltage at the Throttle Position Sensor

1. Disconnect the P403 connector.

2. Turn the keyswitch to the ON position.

3. Measure the voltage between terminals P403-A and P403-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 within specifications. The supply voltage is reaching the sensor. Proceed to Test Step 3.

• Not OK - The supply voltage is incorrect.

  Repair: The configuration of the wiring between the keyswitch 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 3. Check the Signal Wire for a Short Circuit

1. Remove electrical power from the ECM.

2. Disconnect the P1 connector from the ECM.

   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 P1-66 and all of the other terminals in the P1 connector. Also, measure the resistance between terminal P1-66 and the engine ground stud.

Expected Result:

Each resistance measurement indicates an open circuit.

Results:

• OK - Each resistance measurement indicates an open circuit. The signal wire is not shorted to another wire in the harness. Proceed to Test Step 5.

• Not OK - At least one resistance measurement does not indicate an open circuit.

  Repair: The signal wire for the throttle position sensor is shorted to another wire in the harness. The problem could be in the harness 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 4. 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 P1-66 and terminal C (throttle sensor signal) of the throttle sensor's harness connector.

Expected Result:

The resistance measurement indicates that continuity exists in the signal wire.

Results:

• OK - The measurement indicated that continuity exists in the signal wire. Connect the throttle sensor's harness connector. Proceed to Test Step 5.

• Not OK - The resistance measurement indicated that an open circuit or excessive resistance existed in the circuit.

  Repair: There is a problem with the signal wire. 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 5. Check the Frequency of the Throttle Position Signal at the ECM

1. Connect the Caterpillar Electronic Technician (ET) to the service tool connector. Refer to Troubleshooting, "Electronic Service Tools".

2. Connect a 208-0059 Adapter Cable As (70-PIN BREAKOUT) between the P1 connector and the J1 connector.

3. Connect a multimeter between terminal 66 (throttle sensor signal) and terminal 61 (-Battery) on the breakout t.

4. Restore electrical power to the ECM.

5. 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.

6. Observe the "Active Diagnostic" screen on Cat ET. 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.

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. Turn the keyswitch to the off position.

  2. Remove the 208-0059 Adapter Cable As (70-PIN BREAKOUT).

  3. Connect the J1/P1 connectors.

  4. Restore electrical power to the ECM.

  5. 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. Turn the keyswitch to the off position.

  2. 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