HEADLINER 2616778 - 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.Note: Some of the following codes may not be applicable for certain applications.
Table 1
Diagnostic Codes Table
CDL Code Code Description Comments
91-3 Throttle Position Sensor : Voltage Above Normal The Electronic Control Module (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 Throttle Position Sensor : 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 Throttle Position Sensor 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. The throttle position sensor is mounted to a pedal assembly that allows the operator to control the speed of the engine. The geometry of the pedal assembly controls both the travel of the sensor and the range of the output signal. The throttle position sensor cannot be adjusted.The output from the throttle position sensor is a PWM signal that varies with the position of the throttle pedal. The throttle position sensor produces a minimum duty cycle in the released position and a maximum duty cycle in the fully depressed position. When the pedal is released, the ECM translates the sensor output signal to a throttle position of 0 percent. When the pedal is fully depressed, the ECM translates the output signal to a throttle position of 100 percent.
Illustration 1 g02075215
Schematic for throttle position sensor
Illustration 2 g01214474
P1 ECM connector
(P1-4) 8 VDC supply
(P1-5) Digital return
(P1-66) Throttle position
Table 2
Troubleshooting Test Steps Values Results
1. Check the Signal Frequency and the Duty Cycle at the Sensor
A. Turn the keyswitch to the OFF position.
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 the OFF position.
H. Remove the breakout harness. Restore the wiring for the harness connector to the original configuration.
Signal Frequency
Result: The frequency and the duty cycle are within specifications for the entire range of the