Throttle Position Sensor: Essential for Smooth Driving

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Purpose

The Throttle Position Sensor (TPS) monitors the position of the throttle as it opens and closes, as well as the rate at which the throttle is opening or closing, and generates an output signal representing the current position of the throttle. The vehicle's computer uses this information to monitor engine load, acceleration and deceleration, and to determine when the engine is at idle or at wide open throttle, and to make adjustments to fuel mixture and ignition timing based on engine needs.

Some vehicles may also employ a separate idle switch and/or wide open throttle (WOT) switch in conjunction with the throttle position sensor, to provide an indication of when the throttle is at these positions.

Location

The location of the throttle position sensor depends on whether it is rotary-actuated or linear-actuated. Rotary-actuated sensors are generally mounted on throttle body or connected to throttle shaft. Linear-actuated sensors are mounted inside or outside the carburetor.

Operation

The throttle position sensor is essentially a variable resistor (potentiometer). The potentiometer shaft is connected to the vehicle’s throttle. The sensor sends a voltage signal to the vehicle's computer to indicate throttle position.

The voltage increases as the throttle is opened. The computer adjusts air/fuel ratio, spark advance, and idle speed based on throttle position. The sensor actuator may be a rotary actuator (for fuel injected engines) or linear (push) actuator (for carbureted engines).

Idle / Wide Open Throttle Switches

Some vehicles may employ a separate idle switch and/or wide open throttle (WOT) switch in conjunction with the throttle position sensor. These switches may be of the "normally open" or "normally closed" type.

The idle switch signals the vehicle's computer when the throttle is either "at idle" or "off idle." A change in the status of the switch indicates a change in the status of the throttle. The vehicle's computer uses the "at idle" indication for such functions as actuating idle speed control and inhibiting operation of the EGR valve and/or canister purge.

The wide open throttle switch signals the vehicle's computer when the throttle is fully open. The vehicle's computer generally uses the wide open throttle signal to "enrich" the air/fuel mixture for maximum power.

Drivability Symptoms

A malfunction in the throttle position sensor or circuit will cause a faulty signal (or no signal) to be transmitted to the vehicle’s computer. In such a case, the vehicle’s computer cannot accurately determine the position of the throttle.

The computer will attempt to regulate the fuel based on input from the oxygen sensor feedback circuit, however, fuel mixture adjustments will not be as timely, and some drivability problems may occur. The following symptoms may indicate a damaged or defective throttle position sensor, or trouble in a related system:

• Stalling, stumbling or rough idle (due to a "lean" fuel mixture at open throttle conditions)
  
• Hesitation
  
• Air/fuel ratio problems (fuel mixture is excessively "rich" or excessively "lean")
  

Drivability symptoms due to a bad throttle position sensor can be similar to symptoms caused by a bad MAP sensor. Be sure to investigate both areas before parts replacement.

Testing

Use a digital voltmeter to verify proper operation of the throttle position sensor, as follows. Refer to the vehicle’s service manual for throttle position sensor specifications.

NOTE: It may be necessary to disconnect the wiring harness from the throttle position sensor and jumper the POWER and GROUND pins from the harness to the sensor in order to facilitate access to the SIGNAL pin for testing. Be sure to jumper the pins properly.

• Make sure the vehicle's ignition is off.
• Set the voltmeter to the 5V scale.
• Connect the black lead of the voltmeter to the battery negative terminal (ground). Connect the red lead of the voltmeter to the throttle position sensor’s SIGNAL pin.
  
  NOTE: These are typical connector illustrations. Refer to the vehicle's service manual to verify connections.
  
• Turn the ignition on. DO NOT START THE ENGINE.
• Slowly open and close the throttle, and observe the voltmeter indication.
• Verify that the voltage rises smoothly from about 1 volt at "idle" position to a maximum of 5 volts at "wide open throttle."
• Turn the ignition off. Disconnect the voltmeter from the throttle position sensor. Reconnect the wiring harness to the throttle position sensor connector.

Troubleshooting

A loose throttle position sensor will generate an erratic output signal. The vehicle's computer will read this signal as if the throttle is opening and closing. This condition can result in unstable idle and intermittent hesitation.

A short in the throttle position sensor will cause the vehicle's computer to read a constant wide open throttle signal condition, resulting in a fuel mixture that is too "rich."

An open circuit in the throttle position sensor will cause the vehicle's computer to read a constant "closed" throttle position, resulting in fuel mixture that is too "lean."

Some vehicles may employ a separate idle switch and/or wide open throttle (WOT) switch in conjunction with the throttle position sensor. If these components are in use, confirm their functionality before determining a defective throttle position sensor.

Repair/Replacement

The BARO sensor is a sealed unit. If you determine it is defective, it must be replaced. No repair or adjustment Most older throttle position sensors require an initial voltage adjustment following installation to ensure accurate sensing and signaling of throttle position.

While periodic adjustment of the throttle position sensor is generally not necessary, check this setting before part replacement. The specific "base" voltage setting for the throttle position switch varies greatly between vehicle makes and models, as does the manner in which the sensor is adjusted. Refer to the vehicle's service manual for adjustment requirements.is possible.

The throttle position sensor is a sealed unit. If you determine it is defective, it must be replaced. No repair is possible.

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