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Caution: DO NOT attempt to measure resistance of the TPS. To do so can cause catastrophic damage to the sensor.


not 12 volts from the chassis system. The throttle position sensor runs at a fixed frequency and amplitude. The 8 volts remain the same, as does the frequency, throughout the full range of pedal movement: the only thing that changes is the number of pulses within an extremely short period of time. The internal circuitry in the sensor causes a variation in the pulse width in the frequency, depending on the position of the accelerator pedal.

The output signal from the sensor to the ECM is referred to as the Duty Cycle or Pulse Width Modulation, and is expressed as a percentage between 3 and 100%.

At Low Idle the sensor will produce a duty cycle of 10-22%. At Full Throttle it will be 75-90%. This sensor-produced duty cycle is translated in the ECM which determines the timing and amount of fuel delivered to the cylinders.

Throttle Position Sensor Test Procedure

To test the TPS for being functional a meter that measures frequency and duty cycle is required, such as the FLUKE model 87. This particular meter is also a volt/ohm meter.

  • 1.

    Ignition switch must be OFF.

  • 2.

    Disconnect the harness connector going to the throttle sensor, not any other connector. (This connector is located behind the left side windshield wiper motor access door.)

  • 3.

    Install a "breakout" T harness between the sensor and the chassis harness.

  • 4.

    Turn Ignition switch ON.

  • 5.

    Set the meter to % Duty Cycle position. Measure the duty cycle across Ground (pin B) and Signal (pin C).

  • 6.

    Closed throttle reading should be 10-22%. Full throttle should be 75-90%.

If the percentage figures fall within these ranges, the sensor is good.

The same test can be made using the Caterpillar Electronic Analyzer and Programmer toll, their model #8T9697 and tool #8C9801 PWM Signal Adapter.

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