HEAD 1073950 - Caterpillar

Use this procedure to troubleshoot the electrical system if a problem is suspected with the throttle signal from the PWM signal convertor. Also, use this procedure if the diagnostic code in Table 1 is active or easily repeated.
Table 1
Diagnostic Codes Table
CDL Code and 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 5 seconds. The code is logged. The direct fuel control mode enables the engine to be controlled by an external governor. Install the components of the signal converter for the direct fuel control in order to operate in direct fuel control mode. The "Direct Fuel Control Mode" parameter must be programmed to "Enabled" 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
Illustration 1 g03001778
Schematic for the direct fuel control mode (typical example)
Table 2
Troubleshooting Test Steps Values Results
1. Inspect Electrical Connectors and Wiring
A. Turn the main disconnect switch to the OFF position.
B. Thoroughly inspect the ECM connectors J1/P1. Inspect all of the other connectors in the circuit. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
C. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the circuit.
D. Check the allen head screw on each ECM connector for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.
E. Check the harness and the wiring for abrasion and for pinch points.
Connectors
Results: The connectors and wiring are OK.
Proceed to Test Step 2
Results: The connectors and/or wiring are not OK.
Repair: The connectors or wiring and/or replace the connectors or wiring.
Verify that the repair eliminates the problem.
2. Check the Current Input to the Signal Converter
A. Restore the electrical power to the ECM.
B. Measure the current to the signal converter.
Note: Some external governors may only be able to output approximately 150 mA. Do not recognize this output as a problem with the external governor.
0 to 200mA
Results: The current is within the correct range.
Proceed to Test Step 3
Results: The current is not within the correct range.
Repair: Replace the external governor that is supplying the controlling current.
Verify that the repair eliminates the problem.
3. Check the Voltage at the Battery
A. Turn the main disconnect switch to the OFF position.
B. Measure no-load battery voltage at the battery terminals. Refer to Systems Operation/Testing and Adjusting, "Test Tools