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.
The throttle position sensor eliminates the mechanical throttle and governor linkages. The sensor that is installed depends on the engine's configuration.
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| Illustration 1 | g01123466 |
Electronic throttle position sensor | |
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| Illustration 2 | g01122049 |
Throttle position sensor with a lever | |
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| Illustration 3 | g01122050 |
Throttle position sensor with a knob | |
Refer to Illustration 4. 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.
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| 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 091-08 diagnostic code.
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| Illustration 5 | g01130029 |
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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. |
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Test Step 1. Inspect the Electrical Connectors and the Wiring
- Turn the keyswitch to the OFF position.
- Thoroughly inspect connectors (1) and (2). Inspect the connections on the throttle position sensor. Refer to Troubleshooting, "Electrical Connectors - Inspect".
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| Illustration 6 | g01146374 |
Left side engine view (typical example) (1) J1/P1 ECM connector | |
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| Illustration 7 | g01146383 |
Left side engine view (typical example) (2) P61 Customer connector | |
- Perform a 45 N (10 lb) pull test on each of the wires that are associated with the throttle position sensor.
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| Illustration 8 | g01122213 |
P1 terminal that is associated with the throttle position sensor (P1-66) Throttle position | |
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| Illustration 9 | g01122217 |
J61 and P61 terminal that is associated with the throttle position (10) Throttle position | |
- 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.
- 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 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 properly connected. Verify that the repair eliminates the problem.
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Test Step 2. Check for Supply Voltage at the Throttle Position Sensor
- Disconnect the P403 connector.
- Turn the keyswitch to the ON position. The engine should be off.
- 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 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 3.
- 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.
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Test Step 3. Check the Signal Wire for a Short Circuit
- Turn the keyswitch to the OFF position.
- Disconnect the P1 ECM connector.
- Measure the resistance between terminal P1-66 and all of the other terminals in the P1 ECM connector.
Note: Be sure to wiggle the harnesses during the following measurements. Be sure to wiggle each harness near each connector.
Expected Result:
Each resistance measurement indicates an open circuit.
Results:
- OK - Each resistance measurement indicates an open circuit. Proceed to Test Step 5.
- 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 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 P403-C.
Expected Result:
The resistance measurement is less than ten Ohms.
Results:
- OK - The resistance measurement is less than ten Ohms. Connect the P403 connector. Proceed to Test Step 5.
- 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 5. Check the Frequency of the Throttle Position Signal at the ECM
- Connect the Caterpillar Electronic Technician (ET) to the service tool connector. Refer to Troubleshooting, "Electronic Service Tools".
- Connect a 208-0059 Adapter Cable As (70-Pin Breakout) between the P1 ECM connector and the J1 ECM connector.
- Connect a multimeter between terminals 66 on the breakout t and the engine ground stud.
- Turn the keyswitch to the ON position.
- 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.
- 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:
- Turn the keyswitch to the off position.
- Remove the 208-0059 Adapter Cable As (70-Pin Breakout).
- Connect the J1/P1 ECM connector.
- Turn the keyswitch to the ON position.
- 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.
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- Not OK - The frequency of the signal is incorrect. A 91-08 diagnostic code is activated.
Repair: Perform the following procedure:
- Turn the keyswitch to the OFF position.
- Replace the throttle position sensor. Check for a 091-08 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