PIN AS 6S3474 - Caterpillar

System Operation Description:Use this procedure to troubleshoot the electrical system if a problem is suspected with the circuit that is for the throttle position sensor. Also use this procedure if the diagnostic code in Table 1 is active or easily repeated.
Table 1
Diagnostic Codes Table    
Code and Description     Conditions that Generate the Code     System Response    
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.    The load sharing module provides a throttle signal to the engine ECM. The output for rated speed is a Pulse Width Modulated signal (PWM) at a constant frequency. The speed signal varies with the position of the speed adjust potentiometer. The output signal is referred to as a duty cycle or as a PWM signal. The output signal is expressed as a percentage between 0 and 100 percent for the speed adjust.Note: Desired speed can be adjusted from 1141 to 1621 rpm over the range of the PWM signal for a 50 Hz application. For a 60 Hz application, the desired speed can be adjusted from 1369 to 1945 rpm over the range of the PWM signal.The ECM calculates the desired engine rpm from the throttle signal and the droop signal. The throttle signal is valid when the duty cycle is in the range of 5 to 95 percent. If the ECM determines that the throttle signal is invalid, the engine rpm is set to rated speed and the droop percentage will be applied.Note: This engine has an option that supports direct fuel control mode. The direct fuel control mode enables the engine to be controlled by an external governor. To operate in direct fuel control mode, a signal convertor must be installed on the application. Ensure that the "Direct Fuel Control Mode" parameter is programmed to "Disababled". The ECM will then be configured for a control strategy that supports the speed control.
Illustration 1 g02211673
Schematic of the circuit for the speed controlTest Step 1. Inspect the Electrical Connectors and the Wiring
Remove electrical power from the ECM.
Illustration 2 g02164341
Location of the J1/P1 ECM connectors (typical engine view) (1) J1/P1 ECM connectors
Thoroughly inspect connectors (1) and (2). Also, thoroughly inspect all of the other connectors that are in the circuit. Refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect" for details.