Use this procedure to troubleshoot the electrical system if a problem is suspected with the throttle position sensor. Or, use this procedure if the diagnostic code in Table 1 is active.
| Diagnostic Codes Table | ||
|---|---|---|
| Code and Description | Conditions which Generate this Code | System Response |
| 91-8 Throttle Position Sensor : Abnormal Frequency, Pulse Width, or Period | The Engine Electronic Control Module (ECM) detects a sensor frequency that is less than 150 Hz. Or, the engine ECM detects a sensor frequency that is greater than 1000 Hz for two seconds. or The engine ECM detects a duty cycle that is less than 5 percent. Or, the engine ECM detects a duty cycle that is greater than 95 percent for one second. |
The throttle signal defaults to a zero percent duty cycle. |
The throttle position sensor provides a throttle position signal to the engine ECM. The pedal mounted throttle position sensor is attached directly to the assembly. The pedal mounted throttle position sensor cannot be adjusted.
The engine ECM receives a pulse width modulated signal from the throttle position sensor. The ECM converts the duty cycle of the signal into a usable throttle position. The duty cycle must be between 5 percent and 95 percent for a valid signal. The frequency of the signal must be a fixed frequency between 150 Hz and 1000 Hz. The ECM displays the throttle position as a percentage between 0 and 100 percent.
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| Illustration 1 | g02581502 |
Typical schematic | |
Test Step 1. Inspect the Electrical Connectors and the Wiring
- Turn the keyswitch to the OFF position.
- Thoroughly inspect the J1/P1 ECM connectors, the machine connectors, and the connectors for the throttle position sensor. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
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| Illustration 2 | g01234146 |
Location of ECM connectors | |
- Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector and the sensor connectors that are associated with the active diagnostic code.
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| Illustration 3 | g01573106 |
P1 ECM connector (P1-4) +8 V digital supply (P1-5) Digital return (P1-10) Throttle signal | |
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| Illustration 4 | g02581505 |
Machine Connector (Terminal 17) +8 V digital supply (Terminal 36) Digital return (Terminal 19) Throttle position | |
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| Illustration 5 | g01159881 |
Terminal locations at the connector for the throttle position sensor (Terminal A) +8 V digital supply (Terminal B) Digital return (Terminal C) Throttle position | |
- Check the allen head screw for each of the ECM connectors and the machine connectors 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 sensor back to the ECM.
Expected Result:
All connectors, pins, and sockets are inserted and coupled. 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 - There is a problem in the connectors and/or wiring.
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 coupled.Verify that the repair eliminates the problem.
STOP
Test Step 2. Inspect the Throttle Assembly
- Inspect the throttle assembly for components that are loose, bent, missing, or worn.
- Operate the throttle assembly through the full range of motion.
Expected Result:
The throttle assembly operates smoothly without excessive drag. The throttle assembly returns to the low idle position without assistance in less than one second.
Results:
- OK - The throttle assembly is operating correctly. Proceed to Test Step 3.
- Not OK - The throttle assembly is not operating correctly.
Repair: Repair the throttle assembly or replace the throttle assembly. The throttle assembly should return to the low idle position without assistance in less than one second.
STOP
Test Step 3. Check the Status for "Throttle Position"
- Connect Caterpillar Electronic Technician (ET) to the service tool connector.
- Turn the keyswitch to the ON position.
- Observe the status for "Throttle Position" on Cat ET while you operate the throttle.
- Turn the keyswitch to the OFF position.
Expected Result:
The throttle position reads 0 percent when the throttle pedal is released. The throttle position 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 in the harness or in a connector. If an intermittent problem is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect" for information that is related to troubleshooting the problem.
STOP
- Not OK - The status is not correct on Cat ET. There may be a problem with the throttle position sensor. Proceed to Test Step 4.
Test Step 4. Check the Supply Voltage at the Sensor
- Disconnect the connector for the throttle position sensor.
- Turn the keyswitch to the ON position.
- Measure the voltage between terminals A and B on the harness side of the sensor connector.
- Turn the keyswitch to the OFF position.
Expected Result:
The voltage is 8.0 ± 0.4 VDC.
Results:
- OK - The voltage is 8.0 ± 0.4 VDC. The voltage is correct. Proceed to Test Step 5.
- Not OK - The voltage is not 8.0 ± 0.4 VDC. Proceed to Test Step 8.
Test Step 5. Check the Signal Frequency and the Duty Cycle at the Sensor
- Remove the wire from terminal C (signal) on the harness side of the connector for the throttle position sensor.
- Install a 7X-6370 Adapter Cable As (3-PIN BREAKOUT) at the connector. Connect the connectors for the sensor.
- Turn the keyswitch to the ON position.
- Use a multimeter to measure the signal frequency and the duty cycle. Measure between terminal B (digital return) and terminal C (signal) at the breakout while you operate the throttle pedal.
- Turn the keyswitch to the OFF position.
- Remove the breakout from the circuit. Restore the wiring to the original configuration.
Expected Result:
The frequency is between 150 and 1000 Hz. The duty cycle is between 5 percent and 95 percent.
Results:
- OK - The signal frequency and the duty cycle are correct. The sensor is producing a valid signal. Proceed to Test Step 6.
- Not OK - The signal frequency and/or the duty cycle are not correct.
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
- Disconnect the J1/P1 ECM connector.
- Remove the wire from terminal location P1-10 (throttle position) at the ECM connector.
- Connect the J1/P1 ECM connector.
- Turn the keyswitch to the ON position.
- Measure the frequency and the duty cycle. Measure between the wire from terminal P1-10 (throttle position) and terminal P1-5 (digital return) at the breakout while you operate the throttle pedal.
- Turn the keyswitch to the OFF position.
- Restore the wiring to the original configuration.
Expected Result:
The frequency is between 150 and 1000 Hz. The duty cycle is between 5 percent and 95 percent.
Results:
- OK - The signal frequency and the duty cycle are correct. A valid sensor signal is reaching the ECM. Proceed to Test Step 7.
- Not OK - The signal frequency and/or the duty cycle are not correct.
Repair: A valid sensor signal is not reaching the ECM. There is a problem in the harness between the sensor connector and the ECM connector. Repair the wiring harness and/or the connectors. Verify that there is not an open circuit at the machine connector. Verify that the repair eliminates the problem.
STOP
Test Step 7. Check the Status for "Throttle Position"
- Turn the keyswitch to the ON position.
- Observe the status for "Throttle Position" on Cat ET while you operate the throttle pedal.
Expected Result:
The status reads approximately 0 percent when the throttle pedal is released. The status progressively increases to 100 percent when the throttle pedal is fully depressed.
Results:
- OK - The status for "Throttle Position" is correct.
Repair: The throttle position sensor is working properly at this time. There may be an intermittent electrical problem in the wiring harness or in a connector. If an intermittent problem is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect" for information that is related to troubleshooting intermittent electrical problems.
STOP
- Not OK - The status for "Throttle Position" is not correct.
Repair: A valid signal is available to the ECM, but the ECM is not detecting the signal properly. There is a problem with the ECM. Replace the ECM. Refer to Troubleshooting, "ECM - Replace" before replacing the ECM.
STOP
Test Step 8. Check the 8 V Supply Voltage at the ECM
- Disconnect the J1/P1 ECM connector.
- Fabricate two jumper wires that are long enough to be used to measure the supply voltage at the ECM connector. Crimp connector sockets to one end of each jumper wire.
- Remove the wires from terminal locations P1-4 (8 V sensor supply) and P1-5 (sensor return). Install a jumper wire into each of these terminal locations.
- Connect the J1/P1 ECM connector.
- Turn the keyswitch to the ON position.
- Measure the voltage between the jumper wire in P1-4 (8 V sensor supply) and P1-5 (sensor return).
- Turn the keyswitch to the OFF position. Replace all wires and connectors to the original configuration.
Expected Result:
The voltage measurement is 8.0 ± 0.4 VDC.
Results:
- OK - The voltage measurement is 8.0 ± 0.4 VDC. The ECM is operating correctly.
Repair: The supply wire or the return wire has an open circuit. Repair the wire. Verify that there is not an open circuit at the machine connector.
STOP
- Not OK - The voltage measurement is not 8.0 ± 0.4 VDC.
Repair: Replace the ECM. Refer to Troubleshooting, "ECM - Replace".
STOP