Use this procedure to troubleshoot the electrical system if a problem is suspected with the throttle position sensor or if the diagnostic code in Table 1 is active or easily repeated.
| 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 Electronic Control Module (ECM) detects an incorrect frequency on the throttle signal or an incorrect duty cycle on the throttle signal. The frequency is below 150 Hz or the frequency in above 1000 Hz. The duty cycle is less than 5 percent or the duty cycle is greater than 95 percent. | The ECM flags the throttle position as invalid data and a default value of zero percent is used. The engine speed is limited to low idle. |
The primary throttle signal to the engine's ECM is from terminal BN on the customer connector or from terminal BN on the connector for the EMCP electronic control. The throttle signal should be a 500 Hz constant frequency signal with a pulse width that varies with the throttle signal. This output signal is referred to as a Pulse Width Modulated signal (PWM).
The throttle signal's duty cycle should be between 5 percent to 10 percent at low idle and 90 percent to 95 percent at high idle. The percent duty cycle is translated in the ECM into the throttle position of 0 percent to 100 percent.
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| Illustration 1 | g01630073 |
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Typical example | |
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| Illustration 2 | g00725481 |
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Throttle Position Versus PWM Input | |
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| Illustration 3 | g01630153 |
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C-C18/(TB-C1 customer or L-C1/L-C2 EMCP 3) connectors (Terminal BN) Primary throttle signal | |
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| Illustration 4 | g01622856 |
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Connector locations (1) A-C1/E-C2/E-C1 Right hand cross over harness (2) A-C2/J-C2/J-C1 Right hand cross over harness (3) A-C90/P-C1 Connectors for the power distribution panel (4) A-C91/P-C2 Connectors for the power distribution panel (5) A-C60 Connector for the prelube motor (6) A-C92/F-C1/F-C2/G-C6 Connectors for a RH Control panel (7) C-C22 Primary ECM connector P2 (8) C-C15 Primary ECM connector P1 (9) C-C28 Secondary ECM connector P2 (10) C-C29 Secondary ECM connector P1 (11) C-C47 Connector for the power relay panel (12) C-C17/F-C1/F-C2/G-C6 Connectors for a LH Control panel (13) C-C18/(TB-C1 customer or L-C1/L-C2 EMCP 3) connectors (14) C-C2/J-C1/J-C2 Left hand cross over harness (15) C-C1/E-C1/E-C2 Left hand cross over harness | |
Test Step 1. Inspect the Electrical Connectors and the Wiring
- Turn the Engine Control Switch (ECS) to the OFF position.
- Thoroughly inspect the ECM connector J1/P1. Inspect the wiring and the connectors that are associated with the circuit. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
- Perform a
45 N (10 lb) pull test on each of the wires in the ECM connectors that are associated with the circuit. - Check the ECM connector (allen head screw) for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
- Check the harness and wiring for abrasion and for pinch points from the sensors back to the ECM.
Expected Result:
All connectors, pins, and sockets are completely coupled and/or inserted, and the harness and wiring are free of corrosion, of abrasion or of pinch points.
Results:
- OK - The connectors and wiring are OK. Proceed to Test Step 2.
- Not OK - The connectors and/or wiring need repair.
Repair: Repair the connectors or wiring and/or replace the connectors or wiring.
STOP
Test Step 2. Check the Throttle Position on Caterpillar Electronic Technician (ET)
- Connect Cat ET to the service tool connector.
- Turn the ECS to the STOP position.
- Observe the position of the throttle on Cat ET.
- Adjust the throttle to the lowest setting.
- Start at the lowest position. Slowly adjust the throttle to the highest setting. Monitor the position of the throttle on Cat ET.
Expected Result:
The throttle position on Cat ET is 0 percent at the lowest setting and 0 to 100 percent as the throttle is adjusted to the highest setting.
Results:
- OK - The throttle is operating correctly.
Repair: There may be an intermittent problem. If the problem is intermittent, refer to Troubleshooting, "Electrical Connectors - Inspect" for details on inspecting wiring and connectors.
STOP
- Not OK - The throttle position on Cat ET does not change correctly. Proceed to Test Step 3.
Test Step 3. Check the Signal Frequency and the Duty Cycle at the Customer Connector or at the Connector for the EMCP Electronic Control
- Turn the ECS to the OFF position.
- Remove the wire for the throttle signal from the terminal BN on the customer connector or from terminal BN on the connector for the EMCP electronic control. Refer to Illustration 1 for the schematic of the circuit.
- Measure the frequency and the duty cycle of the throttle signal. Adjust the throttle from the lowest position to the highest position.
- Replace all connectors and wires.
Expected Result:
The duty cycle is between 5 to 95 percent. The frequency reading is approximately 500 Hz.
Results:
- OK - The duty cycle and the frequency are correct. Proceed to Test Step 4.
- Not OK - The duty cycle reading is not correct or the frequency is not correct. The throttle position signal is not reaching the ECM.
Repair: Check the signal from the customer's throttle.
STOP
Test Step 4. Check the Duty Cycle at the ECM Connector
- Disconnect the J1/P1 ECM connector from the primary ECM and the secondary ECM.
- Set the multimeter to "VDC". Press the "Hz" button twice so that the % symbol is displayed.
- Place the red probe of the multimeter on terminal P1-10 on the primary ECM connector. Place the black probe of the multimeter on the −Battery terminal.
- Measure the percent duty cycle of the throttle signal. Move the throttle from the lowest setting to the highest setting.
- Repeat the above steps for throttle signal to the secondary ECM.
- Replace all connectors and wires.
Expected Result:
The duty cycle is 5 to 10 percent at the lowest setting. The duty cycle is 90 to 95 percent at the highest setting.
Results:
- OK - The duty cycle and the throttle signal are correct.
Repair: Temporarily replace the ECM and perform the test again. If the problem is resolved, the ECM is faulty. Permanently replace the ECM. Refer to Troubleshooting, "ECM - Replace".
STOP
- Not OK - The duty cycle reading is not correct. The throttle signal is not reaching the ECM.
Repair: Repair the wire between the ECM connector and the customer connector.
STOP