Use this procedure in order to troubleshoot the electrical system if a problem is suspected with the throttle signal. Use this procedure if the diagnostic code in Table 1 is active or easily repeated.
| Diagnostic Codes Table | ||
|---|---|---|
| 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 abnormal throttle signal for five seconds. | The code is logged. |
The direct fuel control mode enables the engine to be controlled by an external governor. You must install the components of the signal converter for the direct fuel control in order to operate in direct fuel control mode. The configuration parameter must be programmed to "ON" in order for the ECM to respond properly to the external governor.
The input to the signal converter is a 0 to 200 mA signal. The signal is received from the external governor. The output signal from the signal converter is a Pulse Width Modulated signal (PWM).
The output signal varies with the current to the signal converter. The ECM calculates the desired fuel from the PWM signal.
The duty cycle for a valid signal is between 5 and 95 percent. If an invalid signal is received, the engine will automatically be set to a minimum fuel setting and the engine will shut down.
The following functions are not used in direct fuel control mode.
- Low idle
- Crank terminate speed
- Cooldown speed
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| Illustration 1 | g01528625 |
Typical example | |
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| Illustration 2 | g01528630 |
Location of the ECM connector (1) J1/P1 ECM connectors | |
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| Illustration 3 | g01528623 |
P1 ECM connector (P1-66) Desired fuel (P1-05) Sensor return | |
Test Step 1. Inspect Electrical Connectors and Wiring
- Turn the Engine Control Switch (ECS) to the OFF/RESET position. Turn the main disconnect switch to the OFF position.
- Thoroughly inspect the ECM connectors J1/P1 and J2/P2. Inspect all of the other connectors in 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 connector that are associated with the circuit.
- Check the allen head screw on each ECM connector for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.
- Check the harness and the wiring for abrasion and for pinch points.
Expected Result:
All connectors, pins, and sockets are completely coupled and/or inserted. The harness and wiring are free of corrosion, of abrasion, and of pinch points.
Results:
- OK - The connectors and wiring are 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.
STOP
Test Step 2. Check the Current Input to the Signal Converter
- Turn the main disconnect switch to the ON position. Turn the ECS to the STOP position.
- Measure the current to the signal converter.
Note: Some external governors may only be able to output approximately 150 mA. This should not be seen as a problem with the external governor.
Expected Result:
The current range is between 0 and 200 mA.
Results:
- OK - The current is within the correct range. Proceed to Test Step 3.
- Not OK - The current is not within the correct range.
Repair: Replace the external governor that is supplying the controlling current.
STOP
Test Step 3. Check the Voltage at the Battery
- Turn the ECS to the OFF/RESET mode. Turn the main disconnect switch to the OFF position.
- Measure no-load battery voltage at the battery terminals. Refer to Systems Operation/Testing and Adjusting, "Test Tools for the Electrical System" for the proper procedures to check the batteries.
- Load test the batteries. Use the 4C-4911 Battery Load Tester. Refer to the Operating Manual, SEHS9249. Refer to Special Instruction, SEHS7633.
Expected Result:
The voltage is 24 ± 3 VDC.
Results:
- OK - The voltage measures 24 ± 3 VDC. Proceed to Test Step 4.
- Not OK - The voltage is not 24 ± 3 VDC.
Repair: The batteries or the alternator are causing the problem. Recharge the batteries or replace the batteries. Verify that the original condition is resolved. Refer to Systems Operation/Testing and Adjusting, "Electrical System".
STOP
Test Step 4. Check the Voltage at the Signal Converter
- Turn the main disconnect switch to the ON position. Turn the ECS to the STOP position.
- Connect one probe of the voltmeter to the +Battery terminal at the signal converter.
- Connect one probe of the voltmeter to the terminal for the sensor return at the signal converter.
Expected Result:
The voltage is 24 ± 3 VDC.
Results:
- OK - The voltage is 24 ± 3 VDC. Proceed to Test Step 5.
- Not OK - The voltage is not 24 ± 3 VDC.
Repair: Check the wiring and/or the connectors that are between the battery and the signal converter. Repair the wiring and/or connectors.
STOP
Test Step 5. Check the Throttle Position
- Connect Caterpillar Electronic Technician (ET) to the service tool connector.
- Turn the ECS to the STOP position.
- Observe the throttle position reading on Cat ET.
- Vary the current to the signal converter.
Expected Result:
The throttle position on Cat ET varies from 0 percent to 100 percent as the current input is adjusted from 0 mA to 200 mA.
Results:
- OK - The throttle position on Cat ET corresponds with the current input.
Repair: Check the system for any diagnostic codes.
STOP
- Not OK - The throttle position does not correspond to the current input. Proceed to Test Step 6.
Test Step 6. Check the Signal from the Signal Converter
- Turn the ECS to the OFF/RESET mode. Turn the main disconnect switch to the OFF position.
- Remove the signal wire from the signal converter.
- Turn the main disconnect switch to the ON position. Turn the ECS to the STOP position.
- Set the multimeter to "VDC".
- Press the "Hz" button twice so that the "%" symbol is displayed.
- Place one probe on the signal wire of the signal converter.
- Place the other probe on the −Battery terminal of the signal converter.
- Monitor the output of the percent duty cycle from the signal converter.
- Adjust the current input from a low current setting to a high current setting.
Note: The throttle position on Cat ET will not match the percent duty cycle on the multimeter.
Expected Result:
The duty cycle is between 5 percent at the low setting and 95 percent at the high setting.
Results:
- OK - The correct signal is being supplied. Proceed to Test Step 7.
- Not OK - The duty cycle is not correct on the multimeter.
Repair: Temporarily install another signal converter. Verify that the problem is no longer present. Reinstall the old signal converter. If the problem returns, replace the signal converter.
STOP
Test Step 7. Check the Signal at the ECM
- Turn the ECS to the OFF/RESET mode. Turn the main disconnect switch to the OFF position.
- Replace the signal wire on the signal converter.
- Remove wire F702-BK from ECM connector P1-66.
- Reconnect ECM connector J1/P1.
- Turn the main disconnect switch to the ON position. Turn the ECS to the STOP position.
- Set the multimeter to "VDC".
- Press the "Hz" button twice so that the "%" symbol is displayed.
- Monitor the output of the percent duty cycle from the signal converter between the signal wire at ECM connector P1-66 and the sensor reference at ECM connector P1-05.
- Vary the input current to the signal converter.
Expected Result:
The duty cycle is between 5 percent at the low setting and above 95 percent at the high setting.
Results:
- OK - The duty cycle is correct.
Repair: Replace the ECM. Refer to Troubleshooting, "ECM - Replace".
STOP
- Not OK-Duty Cycle - The duty cycle is not correct.
Repair: There is a problem in the wiring between the signal wire at ECM connector P1-66 and the signal converter. Repair the wiring or replace the wiring.
STOP