CAGE 8S2123 - 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 Trouble Codes
CDL Code and Description Comments
774-2
Accelerator Pedal Position 2 : Erratic, Intermittent, or Incorrect The Electronic Control Module (ECM) has detected an invalid combination of positions for the multi-position switches.
The code is logged. If equipped, the warning light will come on.
Engine RPM defaults to a predetermined safe speed. The throttle switch is ignored by the ECM until the fault is cleared and the keyswitch is cycled.
774-3
Accelerator Pedal Position 2 : Voltage Above Normal The ECM detects signal voltage that is not in the acceptable range.
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.
774-4
Accelerator Pedal Position 2 : Voltage Below Normal The ECM detects signal voltage that is not in the acceptable range.
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.
774-8
Accelerator Pedal Position 2 : Abnormal Frequency, Pulse Width, or Period The 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.
91-2
Accelerator Pedal Position 1 : Erratic, Intermittent, or Incorrect The ECM has detected an invalid combination of positions for the multi-position switches.
The code is logged. If equipped, the warning light will come on.
Engine RPM defaults to a predetermined safe speed. The throttle switch is ignored by the ECM until the fault is cleared and the keyswitch is cycled.
91-3
Accelerator Pedal Position 1 : Voltage Above Normal The ECM detects signal voltage that is not in the acceptable range.
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.
91-4
Accelerator Pedal Position 1 : Voltage Below Normal The ECM detects signal voltage that is not in the acceptable range.
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.
91-8
Accelerator Pedal Position 1 : Abnormal Frequency, Pulse Width, or Period The 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.
Illustration 1 g02075215
Schematic for throttle position sensor
Probable Causes
Sensor
Sensor supply voltageRecommended Actions
Table 2
Troubleshooting Test Steps Values Results
1. Check the Signal Frequency and the Duty Cycle at the Sensor
A. Turn the keyswitch to OFF.
B. Remove the wire from terminal location C (throttle position) on the harness side