Throttle Position Sensor Problems

by William Norman
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Image by, courtesy of Harry Heng

The throttle position sensor plays an important role in a car or truck's overall performance. This device, which feeds data to the vehicle's computer system and allows it to determine the correct mix of air to fuel for the engine, can either malfunction or receive incorrect information from the throttle components.

Normal Operation

As described by Auto Media, the throttle position sensor relays information about the throttle's status to the vehicle's engine computer, which then compares the information with other factors such as speed, vehicle load and engine temperature in its commands to the vehicle. The throttle position sensor usually relies on a potentiometer, sometimes accompanied by a switch, that sends signals of varying voltage to indicate relative throttle position.

Throttle position sensors can fail or wear out just like any other engine component. Sometimes improper service causes the sensor to malfunction. A sensor problem will usually activate a check-engine light, but the car may send out its own cry for help in the form of performance problems.

Sensor Failure

According to Wells Manufacturing Corporation, a throttle position sensor may malfunction from its initial installation. This installation sets the performance parameters for the sensor, and an incorrect setting will cause the computer to request a less-than-optimum fuel mixture, resulting in poor engine performance from the beginning of the car's life.

Intermittent Errors

A throttle position sensor must issue a steady stream of data to the computer to account for each throttle adjustment. If the throttle position sensor fails to relay a "throttle closed" signal to the computer, the car will stall or experience start-up problems. The car may also hesitate, or misfire while in gear, if the throttle position sensor develops a loose connection, according to Wells Manufacturing Corporation.

"Always Closed" or "Always Open" Errors

Some malfunctions can cause the throttle position sensor to regard the throttle as always open or always closed. A short in the sensor, for instance, will produce the "always-open" error, resulting in an overly rich fuel mixture. If the sensor circuit remains continuously open, the computer will interpret this as an "always-closed" signal and create an overly lean fuel mixture.

Troubleshooting and Repair

Before troubleshooting the throttle position sensor itself, Auto Media recommends checking the throttle components for proper function. If the throttle stop or cables keep the throttle forced open, the sensor cannot tell the computer to put the car into idle.

Auto-Facts states that an automotive scan tool offers an easy way to detect throttle position sensor issues. While some of these tools can only interpret check-engine codes, others can read the actual data stream issuing from the sensor. Depressing the throttle slowly will cause a bad potentiometer to throw an error code. A faulty sensor usually requires replacement, but if the problem lies elsewhere in the engine, repairs to those components may solve the problem.

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