Use this procedure to troubleshoot the electrical system if a problem is suspected with the speed control 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 Engine's Electronic Control Module (ECM) detects a sensor frequency that is less than 150 Hz or a sensor frequency that is greater than 1000 Hz for two seconds. or The ECM detects a duty cycle that is less than 5 percent or a duty cycle that is greater than 95 percent for one second. |
The code is logged. The throttle signal defaults to a zero percent duty cycle (low idle). |
The speed control is used to provide a throttle signal to the engine control. The output from the speed control for rated speed is a pulse width modulated signal. The signal varies with the position of the speed adjust potentiometer. The ECM calculates the desired engine speed from the signal from the speed control. The rated speed signal is valid when the duty cycle is in the range of 5 to 95 percent. If the ECM detects a rated speed signal that is invalid, the engine will be set to low idle.
Some applications may choose not to use the speed control. Some applications may use a load sharing unit. The unit is configured to provide the engine control with a rated speed signal. Some of these units cannot provide a signal until the engine is running. In these cases, perform troubleshooting while the engine is running.
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| Illustration 1 | g01268064 |
Typical schematic | |
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| Illustration 2 | g01268069 |
P1 ECM connector (P1-05) Digital return (P1-10) Primary throttle | |
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| Illustration 3 | g01212010 |
Machine interface connector (Terminal 09) Digital return (Terminal 10) Primary throttle | |
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| Illustration 4 | g01234146 |
Location of ECM connectors | |
Test Step 1. Inspect Electrical Connectors and Wiring
- Turn the switch that provides power to the keyswitch input for the ECM to the OFF position.
- Turn the breaker for the ECM to the OFF position.
- Thoroughly inspect the ECM connector J1/P1. Inspect all of the Connectors in the circuit. Refer to Troubleshooting, "Inspecting Electrical Connectors" for details.
- Check the ECM connector (allen head screw) for the proper torque. Refer to Troubleshooting, "Inspecting Electrical Connectors" 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 harness and the wiring for abrasion and pinch points.
Expected Result:
The components and wiring are free of the following problems: damage, corrosion, abrasion and incorrect attachment.
Results:
- OK - The wiring and connectors are OK. Proceed to Test Step 2.
- Not OK - The wiring and/or connectors need repair.
Repair: Repair the connectors or wiring and/or replace the connectors or wiring.
STOP
Test Step 2. Check the Voltage at the Speed Control
- Connect the red probe of the digital multimeter to the +Battery terminal of the speed control. Connect the black probe of the digital multimeter to the −Battery terminal of the speed control.
Expected Result:
The digital multimeter reads 24 ± 3 VDC.
Results:
- OK - The voltage supply to the speed control is correct. Proceed to Test Step 3.
- Not OK - The digital multimeter did not read 24 ± 3 VDC.
Repair: There is a problem with the supply voltage to the speed control. Verify that any circuit protection is not tripped. Repair any wiring or connections that are damaged.
STOP
Test Step 3. Check the Throttle Position on Caterpillar Electronic Technician (ET)
- Connect Cat ET to the service tool connector.
- Turn the breaker for the ECM to the ON position.
- Turn the switch that provides power to the keyswitch input for the ECM to the ON position.
- Observe the position of the throttle on Cat ET.
- Turn the speed adjust potentiometer to the lowest setting.
- Start at the low idle position. Slowly turn the speed adjust potentiometer in the other direction. Monitor the position of the throttle on Cat ET.
Expected Result:
The throttle position on Cat ET reads 0 percent at the lowest setting and 0 to 100 percent as the speed adjust potentiometer is adjusted.
Results:
- OK - The speed control is operating correctly.
Repair: There may be an intermittent problem. If the problem is intermittent, refer to Troubleshooting, "Inspecting Electrical Connectors".
STOP
- Not OK - The throttle position on Cat ET does not respond to adjusting the speed adjust potentiometer. Proceed to Test Step 4.
Test Step 4. Check the Speed Control
- Remove the wire from the S terminal at the speed control.
- Set the multimeter to "VDC". Press the "Hz" button twice so that the % symbol is displayed.
- Place one probe of the multimeter on the S terminal of the speed control. Place the other probe on the −Battery terminal of the speed control.
- Monitor the output of the percent duty cycle from the speed control on the multimeter. Turn the potentiometer from the low setting to the high setting.
Expected Result:
The duty cycle is between 4 and 10 percent at the low setting and between 90 and 95 percent at the high setting.
Results:
- OK - The speed control is supplying the correct signal. Proceed to Test Step 5.
- Not OK - The duty cycle is not correct on the multimeter.
Repair: Check the speed adjust potentiometer for proper operation. If the speed adjust potentiometer is operating correctly, temporarily install another speed control. Verify that the problem is no longer present.
STOP
Test Step 5. Check the Throttle Signal at the ECM
- Turn the switch that provides power to the keyswitch input for the ECM to the OFF position.
- Turn the breaker for the ECM to the OFF position.
- Remove wire F702-GN from P1-10 at the ECM connector P1.
- Turn the switch that provides power to the keyswitch input for the ECM to the ON position.
- Turn the breaker for the ECM to the ON position.
- Measure the duty cycle between wire F702-GN and P1-5 of ECM connector P1.
Note: 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 speed control on the multimeter. Turn the speed adjust potentiometer from the low setting to the high setting.
- Turn the switch that provides power to the keyswitch input for the ECM to the OFF position.
- Turn the breaker for the ECM to the OFF position. Reconnect all wires and connectors to the original configuration.
Expected Result:
The duty cycle is between 4 and 10 percent at the low setting and between 90 and 95 percent at the high setting.
Results:
- OK - The duty cycle is correct. Proceed to Test Step 6.
- Not OK - The duty cycle is not correct.
Repair: There is a problem in the wiring between P1-10 and the S terminal of the speed control.
STOP
Test Step 6. Check the ECM
- Turn the breaker for the ECM to the ON position.
- Turn the switch that provides power to the keyswitch input for the ECM to the ON position.
- Monitor the percent throttle position on Cat ET. Turn the speed adjust potentiometer from the low setting to the high setting.
Expected Result:
The percent throttle position is between 0 and 100 percent for the above settings of the speed adjust potentiometer.
Results:
- OK - The throttle position on Cat ET is correct. There is an intermittent problem in the wiring and/or connectors between the ECM and the throttle position sensor.
Repair: If the problem is intermittent, refer to Troubleshooting, "Inspecting Electrical Connectors".
STOP
- Throttle Position Not OK - The throttle position is not correct. The ECM is not processing the signal correctly.
Repair: Replace the ECM. Refer to Troubleshooting, "Replacing the ECM".
STOP