CAP AS-DUST 6N1604 - Caterpillar

Use this procedure to troubleshoot a problem with the throttle signal from the PWM signal convertor. Also, use this procedure if the following diagnostic code is active or easily repeated.
Table 1
J1939 Code and Description CDL Code and Description Comments
91-8
Accelerator Pedal Position #1 : Abnormal Frequency, Pulse Width, or Period 91-8
Throttle Position Sensor : Abnormal Frequency, Pulse Width, or Period The Electronic Control Module (ECM) detects an incorrect frequency on the throttle signal or an incorrect duty cycle on the throttle signal.
The code is logged. The ECM flags the throttle position as invalid data and a default value is used. The engine speed is limited to high idle. 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 to operate in direct fuel control mode. The "Direct Fuel Control Mode" parameter must be programmed to "Enabled" in order for the Electronic Control Module (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 shutdown.The following functions are not used in direct fuel control mode.
Low idle
Crank terminate speed
Cooldown speed
Illustration 1 g06193456
Table 2
Troubleshooting Test Steps Values Results
1. Inspect the Electrical Connectors and the Wiring
A. Turn the main disconnect switch to the OFF position.
B. Thoroughly inspect the connectors. Refer to Troubleshooting, "Electrical Connectors-Inspect" for additional information.
C. Perform a 45 N (10 lb) pull test on the connector wires.
D. Check the harness for abrasions and pinch points.
Connectors and Wiring
Result: The connectors and wiring appear to be OK.
Proceed to Test Step 2.
Result: There is a problem with the connectors and/or wiring.
Repair: Repair or replace the connectors or wiring. Ensure that all the seals are properly in place and ensure that the connectors are coupled.
If the problem is not resolved, proceed to Test Step 2.
2. Check the Current Input to the Signal Converter
A. Turn the main disconnect switch to the ON position.
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 mA to 200 mA
Result: The current is within the correct range.
Proceed to Test Step 3.
Result: The current is not within the correct range.
Repair: Replace the external governor that is supplying the controlling current.
Verify that the repair eliminated the problem.
3. Inspect the Batteries
A. Measure no-load battery voltage at the battery terminals. Refer to Testing and Adjusting, Test Tools for the Electrical System for additional information.
B. Charge the batteries, if necessary. Refer to