Use this procedure to troubleshoot the electrical system if a problem is suspected with the throttle signal or 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 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 customer supplied throttle signal provides a 500 Hz pulse width modulated signal (PWM) to the engine's ECM. The signal is expressed as a percentage between 1 and 100 percent. The signal will produce a duty cycle of 5 to 10 percent at the low idle setting. The signal will produce a duty cycle of 90 to 95 percent at the high idle setting. The percent duty cycle is translated by the ECM into a throttle position of 0 to 100 percent.
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| Illustration 1 | g01259642 |
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Typical schematic | |
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| Illustration 2 | g01259643 |
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P1 ECM connector (P1-10) Throttle | |
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| Illustration 3 | g01259644 |
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Connector "A" (Terminal 14) Throttle | |
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| Illustration 4 | g01259645 |
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Connector "F" (Terminal 29) Throttle | |
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| Illustration 5 | g01234146 |
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Location of ECM connectors | |
Test Step 1. INSPECT THE ELECTRICAL CONNECTORS AND THE WIRING
- Turn the breaker for the ECM to the OFF position.
- Thoroughly inspect the ECM connectors J1/P1 and J2/P2. Inspect all of the other connectors. Refer to Troubleshooting, "Inspecting Electrical Connectors" for the proper procedure for inspecting system wiring.
- 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 for each of the ECM connectors for the proper torque. Refer to Troubleshooting, "Inspecting Electrical Connectors" for details.
- 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 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 completely coupled.
STOP
Test Step 2. CHECK THE THROTTLE SIGNAL AT CONNECTOR G ON THE REMOTE JUNCTION BOX
- Remove the wire for the throttle from terminal 29 on connector G in the remote junction box.
- Connect a multimeter between the wire that was removed in the previous test step and engine ground.
- Set the multimeter to "VDC". Press the "Hz" button twice so the "%" symbol is displayed.
- Monitor the duty cycle as you move the throttle from the low idle position to the highest engine speed setting.
- Reconnect all wires.
Expected Result:
The duty cycle is between 5 and 10 percent at the low idle position and between 90 and 95 percent at the highest engine speed setting.
Results:
- OK - The throttle signal from the customer to the remote junction box is OK. Proceed to Test Step 3.
- Not OK - The problem is in the customer supplied throttle position sensor circuit.
Repair: To troubleshoot the customer supplied throttle position sensor, refer to the literature that is supplied by the OEM of the locomotive.
STOP
Test Step 3. CHECK THE THROTTLE SIGNAL AT CONNECTOR A ON THE REMOTE JUNCTION BOX
- Remove the wire for the throttle from terminal 14 on connector A in the remote junction box.
- Connect a multimeter between the wire that was removed in the previous test step and engine ground.
- Set the multimeter to "VDC". Press the "Hz" button twice so the "%" symbol is displayed.
- Monitor the duty cycle as you move the throttle from the low idle position to the highest engine speed setting.
- Reconnect all wires.
Expected Result:
The duty cycle is between 5 and 10 percent at the low idle position and between 90 and 95 percent at the highest engine speed setting.
Results:
- OK - The throttle signal to the ECM from the remote junction box is OK. Proceed to Test Step 4.
- Not OK - The problem is in the remote junction box.
Repair: Repair the wire or the connectors in the remote junction box.
STOP
Test Step 4. CHECK THE THROTTLE SIGNAL AT THE ECM
- Disconnect the J2/P2 ECM connector.
- Measure the duty cycle between wire F702-GN(Green) in P2-10 and engine ground.
Note: Set the multimeter to "VDC". Press the "Hz" button twice so that the % symbol is displayed.
- Monitor the duty cycle with the multimeter.
- Move the throttle from the low idle to the highest engine speed setting.
- Restore the wiring to the original configuration.
Expected Result:
The duty cycle is between 5 and 10 percent at the low idle position and between 90 and 95 percent at the highest engine speed setting.
Results:
- OK - The duty cycle is correct. The throttle signal is present at the ECM. Proceed to test step 5.
- Duty Cycle Reading NOT OK - The duty cycle reading is not correct. There is a problem with the wiring between ECM connector P2-10 and connector A in the remote junction box.
Repair: Repair the wire or the connectors between the remote junction box and the ECM.
STOP
Test Step 5. CHECK THE THROTTLE POSITION WITH CATERPILLAR ELECTRONIC TECHNICIAN (ET)
- Connect Cat ET to the service tool connector.
- Turn the breaker for the ECM to the ON position.
- Observe the throttle position reading on Cat ET.
- Move the throttle to low idle. Slowly move the throttle toward the highest engine speed setting. Monitor the status screen.
Expected Result:
The throttle position reads 0.0 percent when the throttle is in the low idle position. The throttle position reads 100 percent at the highest engine speed setting.
Results:
- OK - The throttle position reads 0.0 percent when the throttle is in the low idle position. The throttle position moves to 100 percent at the highest engine speed setting. The ECM is receiving the throttle signal 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 does not read 0.0 percent when the throttle is in the low idle position. The throttle position does not move to 100 percent at the highest engine speed setting. The ECM is not receiving the throttle signal correctly.
Repair: Replace the ECM. Refer to the diagnostic procedure Troubleshooting, "Replacing the ECM".
STOP