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How to Replace the Throttle Position Sensor System in GMC Vehicles

by Jack Hathcoat

GMC vehicles started using throttle position sensors in the mid 1980s when computerized engine controls were introduced. Of all the sensors on the engine, the throttle position sensor is the only one that communicates driver input to the computer. When the throttle pedal moves, the throttle sensor also moves in direct response to the driver commands. As the throttle moves, a voltage signal ranging from 0.5 volts to 5.0 volts is sent to the engine computer. If the sensor fails, the computer has no precise control over the engine fuel delivery. Replacing the sensor is essential for good performance.

Turn off the engine and raise the hood of the GMC vehicle. In most cases, remove the air cleaner that covers the throttle body. Locate the accelerator linkage. Just opposite the throttle lever, on the opposite side of the throttle body, the throttle position sensor is located. It bolts over the throttle plate shaft and has three wires connected with a snap-in plug. Leave the battery connected. Precise sensor voltage adjustments are necessary when the new sensor is installed.

Unplug the throttle sensor by lifting up the plug clip and pulling directly back on the connector. Unbolt the sensor using a socket to fit the small bolts. These are locked in with thread lock compound, so be careful to keep steady pressure and not strip the bolt heads.

Install a new sensor and loosely fit the mounting bolts into place, Notice how the bolt holes on the sensor are slotted. Tighten the bolts just enough to allow the new sensor to slightly move back and forth for final adjustment. Plug in the sensor connector and clip wire-piercing probes on the center and left wire. Turn on the ignition and set the voltmeter to the 12-volt scale. Adjust the throttle sensor, with the throttle completely closed, to 0.5 volts. Tighten the small bolts.

Replace the air cleaner and lower the hood. Start the GMC and perform a test drive to make sure the system is operating correctly.

Tip

  • When a throttle position sensor fails, the GMC runs, but fuel mileage and performance suffer because an important part of the data stream from the engine management system is interrupted. Everything falls onto other sensors, and the computer makes radical program changes to keep the vehicle running. These changes are known as the limp-in mode, and extended use without repairs will cause extensive damage.

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About the Author

Jack Hathcoat has been a technical writer since 1974. His work includes instruction manuals, lesson plans, technical brochures and service bulletins for the U.S. military, aerospace industries and research companies. Hathcoat is an accredited technical instructor through Kent State University and certified in automotive service excellence.

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  • digital multimeter 3 image by dinostock from Fotolia.com