C13 Engines for Caterpillar Built Machines 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 voltage

Recommended 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 of the connector for the throttle position sensor. C. Install a 326-4904 Adapter Cable As (3-PIN BREAKOUT) at the connector for the throttle position sensor. D. Connect the connector for the throttle position sensor. E. Turn the keyswitch to the ON position. F. Measure the frequency and the duty cycle between terminal B (digital return) and terminal C (throttle position) at the 326-4904 Adapter Cable As (3-PIN BREAKOUT). Operate the throttle pedal while making the measurements. G.Turn the keyswitch to OFF . H.Remove the breakout harness. Restore the wiring for the harness connector to the original configuration.	Frequency Duty Cycle	Result: The ECM detects an incorrect frequency on the throttle signal or an incorrect duty cycle on the throttle signal. The frequency is below 150 Hz or the frequency is above 1000 Hz. The duty cycle is less than 5 percent or the duty cycle is greater than 95 percent. Proceed to Test Step 2. Result: The frequency and the duty cycle are OK. Repair: Repair the harness or replace the harness. If the problem is not resolved, proceed to Test Step 2.
2. Check the Supply Voltage to the Sensor A. Turn the keyswitch to OFF. B. Disconnect the harness connector for the throttle position sensor. C. Measure the voltage across terminal A (8 V supply) and terminal B (digital return) on the harness side of the connector. The voltage should measure 7.5 VDC.	Supply voltage	Result: The supply voltage is above 7.5 VDC at the sensor connector. Repair: The wiring is OK. Replace the sensor. Verify that the problem is resolved. Result: The supply voltage is not above 7.5 VDC at the sensor connector. The supply voltage is not reaching the speed control. Repair: Repair the harness wiring or replace the harness. Verify that the problem is resolved.

If the problem is not resolved, contact your Cat dealer Technical Communicator (TC). For further assistance, your TC can confer with the Dealer Solutions Network (DSN).