CASE AS-TOOL 4C9658 - Caterpillar

System Operation Description: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.
Table 1
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).
Illustration 1 g01258922
Typical schematic
Illustration 2 g01214513
(P2-69) Fuel position multiplier
Illustration 3 g01234146
Location of ECM connectors
Illustration 4 g01258924
Connector "B"
(Terminal 8) Fuel position multiplier
Illustration 5 g01258926
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, "Electrical Connectors - Inspect" for details.
Check the ECM connector (allen head screw) for the proper torque. 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 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