RING-BACKUP 3015241 - Caterpillar

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 one of the diagnostic codes 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 incorrect frequency on the throttle signal or an incorrect duty cycle on the throttle signal.
This code is used when the parameter for the "Desired Speed Input Configuration" is configured to "PWM". The code is logged. The ECM flags the throttle position as invalid data and a default value is used. The engine speed may be limited to high idle. The speed control provides a throttle signal and a droop signal to the 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 for droop is a PWM signal at a constant frequency. The droop signal varies with the position of the droop adjust potentiometer. The output signal is referred to as a duty cycle or as a PWM signal. The output signal of the speed adjust is expressed as a percentage between 0 and 100 percent. The output signal of the droop adjust is expressed as a percentage between 0 and 10 percent.The ECM calculates the desired engine rpm from the rated speed signal and the droop signal. The rated speed signal is valid when the duty cycle is in the range of 5 to 95 percent. If the ECM determines that the rated speed signal is invalid, the engine rpm will be set to the programmed low idle.The droop signal is valid when the duty cycle is in the range of 15 to 85 percent. If the ECM determines that the droop signal is invalid, the engine will run with no droop which is referred to as isochronous mode.Some applications may choose not to use the speed control. Some applications may use a load sharing module. The load sharing module is configured to provide the engine control with a rated speed signal. The signal has the same characteristics as the above defined signal. Some of these load sharing modules cannot provide a signal until the engine is running. In these cases, troubleshooting should be performed while the engine is running.
Illustration 1 g03320984
Typical schematic
Illustration 2 g03323693
Terminal locations at the P1 ECM connector
(P1-5) Digital return
(P1-10) Rated speed signal
Illustration 3 g03323694
Terminal locations at the P2 ECM connector
(P2-69) Speed droop signal
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 connectors (P1), and (P2). Inspect all of the connectors in the harness from the engine interface connector to the speed control that are associated with the circuit. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
C. Perform a 45