SEAL-O-RING 1757898 - 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 Electronic Control Module (ECM) can be configured to receive three different types of throttle signals for the engine throttle control:"CAN Input" - A J1939 signal is received via the CAN data link."PWM" - The Pulse Width Modulated signal (PWM) must be received via terminal P1-66 at the ECM connector. If direct fuel control mode is used on the engine, the PWM signal must be received via terminal P1-66 at the ECM connector.The signals must be present at the respective inputs in order for the signals to be received by the ECM.For using an electronic external governor for engine control, the "Direct Fuel Control Mode" parameter must be enabled. The ECM input at P1-66 must be used for direct fuel control of the engine. Refer to Troubleshooting, "Direct Fuel Control Mode - Test" for details.For information on these parameters, refer to Troubleshooting, "Configuration Parameters". The ECM will utilize the signal that is defined as the primary throttle as long as a valid signal is available from the expected source. If the signal from the primary throttle becomes unavailable, the ECM will use the signal that is defined as the secondary throttle. If both throttle signals become unavailable, the ECM uses the rated speed of the engine as the setpoint for the desired engine speed.From the factory, the ECM is configured to receive the primary throttle via the CAN data link (J1939 broadcast). The secondary throttle is configured at terminal P1-66 of the ECM connector (PWM signal). The speed control provides a PWM signal for the secondary throttle at this location.Two available throttle signals are unused for this application. Refer to Illustration 1. The second is the inputs for the analog throttle at terminal P2-40 primary ECM and P2-16 secondary ECM.
Illustration 1 g03018817
Schematic of the circuit for the speed control
Illustration 2 g02985256
Terminal locations at the P1 ECM connector for the speed control
(P1-66) Throttle 1 (pri. & sec.)
(P1-1) Throttle 2 (pri. & sec.)
Illustration 3 g02985297
Terminal locations at the P2 ECM connector for the speed control
(P2-92) Analog throttle
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