Use this procedure to troubleshoot the electrical system if a problem is suspected with the signal from the fuel position multiplier or if the diagnostic code in Table 1 is active or easily repeated.
| Diagnostic Codes Table | ||
|---|---|---|
| Description | Conditions which Generate this Code | System Response |
| 1177-8 Fuel Position Multiplier 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 engine's ECM detects a duty cycle that is less than 10 percent or a duty cycle that is greater than 90 percent for one second. |
The code is logged. |
The fuel position multiplier is an external input to the ECM. The input reduces the available fuel rack according to the magnitude of the signal. The fuel position multiplier can be considered as an external derating of engine power. Typically, the input is a means for reducing the engine power without changing the throttle signal.
The ECM reads a Pulse Width Modulated signal (PWM) that is similar to the throttle signal. Usually, a converter is used to change the signal from the torque limit control into a PWM signal. An increase in the duty cycle reduces the available fuel. For example, if the engine power output is 100 percent and the signal from the fuel position multiplier is set to 75 percent, the engine power output is reduced to 25 percent.
The fuel position multiplier affects the available fuel rack instantly. The signal is applied in addition to any active derating of the engine power. For example, if the engine is presently derated by 10 percent due to high exhaust temperature and the signal from the fuel position multiplier is 25 percent, the engine power output is reduced by a total of 35 percent. A signal of 10 percent or less will dictate the multiplier to 1.0 (100 percent). A signal of 90 percent to 95 percent will dictate the multiplier to 0.0 (0 percent). A signal of 95 percent or a signal that is greater than 95 percent will dictate the multiplier to 1.0 (100 percent).
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| Illustration 1 | g01258922 |
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Typical schematic | |
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| Illustration 2 | g01214513 |
| (P2-69) Fuel position multiplier | |
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| Illustration 3 | g01234146 |
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Location of ECM connectors | |
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| Illustration 4 | g01258924 |
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Connector "B" (Terminal 8) Fuel position multiplier | |
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| Illustration 5 | g01258926 |
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Connector "G" (Terminal 24) Fuel position multiplier | |
Test Step 1. INSPECT THE ELECTRICAL CONNECTORS AND THE WIRING
- Turn the breaker for the ECM to the OFF position.
- Thoroughly inspect the ECM connector J2/P2. Inspect all of the other connectors. Refer to the diagnostic functional test 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 WIRING FROM THE FUEL POSITION MULTIPLIER
- Disconnect the fuel position multiplier.
- Connect a throttle position sensor or a device that will generate a 500 Hz PWM signal. Connect the attachment directly to the wiring that sends the PWM signal to the ECM.
Note: Remember to remove the sensor and the attachment for the throttle when the test is complete. Reconnect the fuel position multiplier.
- Turn the breaker for the ECM to the ON position.
- Start Caterpillar Electronic Technician (ET).
- Observe the fuel position multiplier and the throttle signal on Cat ET. Set the fuel position multiplier to 0.0. Adjust the throttle from the minimum to the maximum throttle. Record the results.
- Observe the fuel position multiplier and the throttle on Cat ET. Set the fuel position multiplier to 0.5. Adjust the throttle from the minimum to the maximum throttle. Record the results.
- Observe the fuel position multiplier and the throttle on Cat ET. Set the fuel position multiplier to 1.0. Adjust the throttle from the minimum to the maximum throttle. Record the results.
- Turn the breaker for the ECM to the OFF position.
- Restore the wiring to the original configuration.
Expected Result:
The throttle on the Cat ET varies from 0 percent to 100 percent when the fuel position multiplier is set at 0.0. The throttle on the Cat ET varies from 0 percent to 50 percent when the fuel position multiplier is set at 0.5. The throttle on the Cat ET is 0 percent when the fuel position multiplier is set at 1.0.
Results:
- OK - The ECM is reading the throttle signal correctly. The wiring between the fuel position multiplier and the ECM is OK. The ECM is reading the fuel position multiplier correctly.
Repair: The problem appears to be the fuel position multiplier or the connector for the fuel position multiplier. Refer to the OEM manual.
STOP
- Not OK - The ECM is not reading the throttle signal correctly. There is a problem in the wiring between the fuel position multiplier and the ECM. Proceed to Test Step 3.
Test Step 3. CHECK THE SIGNAL INPUT TO THE ECM
- Remove wire G746-WH(White) from ECM connector J2-69.
- Connect a throttle position sensor or a device that will generate a 500 Hz PWM signal. Connect the attachment directly to ECM connector J2-69.
Note: Remember to remove the sensor and the attachment for the throttle when the test is complete. Reconnect the fuel position multiplier.
- Reconnect the ECM connector J2/P2.
- Start Cat ET.
- Turn the breaker for the ECM to the ON position.
- Observe the fuel position multiplier and the throttle signal on Cat ET. Set the fuel position multiplier to 0.0. Adjust the throttle from the minimum to the maximum throttle. Record the results.
- Observe the fuel position multiplier and the throttle on Cat ET. Set the fuel position multiplier to 0.5. Adjust the throttle from the minimum to the maximum throttle. Record the results.
- Observe the fuel position multiplier and the throttle on Cat ET. Set the fuel position multiplier to 1.0. Adjust the throttle from the minimum to the maximum throttle. Record the results.
- Turn the breaker for the ECM to the OFF position.
- Restore the wiring to the original configuration.
Expected Result:
The throttle on Cat ET varies from 0 percent to 100 percent when the fuel position multiplier is set at 0.0. The throttle on Cat ET varies from 0 percent to 50 percent when the fuel position multiplier is set at 0.5. The throttle on Cat ET is 0 percent when the fuel position multiplier is set at 1.0.
Results:
- OK - The ECM is reading the throttle signal correctly. The ECM is reading the fuel position multiplier correctly.
Repair: The problem is in the wiring and/or connectors between the ECM and the fuel position multiplier. Repair the connector and/or wiring or replace the connector and/or wiring.
STOP
- PWM Reading NOT OK - The reading for the fuel position multiplier is not correct on Cat ET.
Repair: The problem appears to be in the ECM. Replace the ECM. Refer to Troubleshooting, "Replacing the ECM".
STOP