How to test a throttle position sensor with a voltmeter

Written by dan swords
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How to test a throttle position sensor with a voltmeter
Diagnose throttle problems with a voltmeter. (digital multimeter image by dinostock from Fotolia.com)

The throttle position sensor (TPS) is used by the electronic control module (ECM) to determine engine speed. When you press on the TPS, the ECM reads the TPS signal and other sensors to determine how much fuel to inject into the cylinder. The most common TPS used is the potentiometer, which outputs a variable voltage depending on the position of the throttle. If the ECM detects a problem with the throttle signal, the ECM will log a P0121 throttle diagnostic code.

Skill level:
Moderate

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Things you need

  • Digital voltmeter
  • Engine electrical schematic
  • Electrical tape
  • Wire removal tool

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Instructions

  1. 1

    Inspect the engine harness and confirm that all connections are tight and secure. Inspect the engine harness for damage, abrasion or corrosion. To temporarily repair a broken or damaged wire, wrap the exposed wire with electrical tape. Remove corrosion with baking soda, water and a wire brush.

  2. 2

    Locate your throttle position sensor. This may be inside the engine compartment, on the intake manifold or on the throttle pedal. Inspect the throttle wiring from the sensor to the electronic control module. Make sure the wires are free of abrasion, damage and corrosion. Inspect the linkage connections and mounting hardware. The linkage should move freely and the throttle sensor should be mounted securely to the bracket or throttle pedal.

  3. 3

    Disconnect the throttle sensor connector. Review the schematic for the engine and locate the throttle +V and ground connection. Turn the ignition to "On." Set the voltmeter to measure voltage. Place the positive probe on the +V or +5 terminal and place the negative probe on ground. The voltage should be approximately 5 volts. If the voltage is not correct, there may be a problem with the ECM sensor supply.

  4. 4

    Turn the ignition to "Off." Refer to the schematic and locate the throttle +V and ground connection on the ECM. Sometimes the ground connection is referred to as "Sensor Common." Set the voltmeter to measure resistance. Place the positive probe on the +V wire on the sensor connector and place the negative probe on the +V connection at the ECM. Wiggle the harness during measurement to reveal an intermittent open condition. The resistance should be less than 5 ohms. Place the positive probe on the ground wire on the sensor connector and place the negative probe on the ground or sensor common wire at the ECM. Wiggle the harness during measurement to reveal an intermittent open condition. The resistance should be less than 5 ohms. If the resistance is greater than 5 volts, there is an open circuit in the wire. Replace the wire and retest.

  5. 5

    Refer to the schematic and locate the throttle signal on the ECM. Place the positive probe on the signal wire on the sensor connector and place the negative probe on the sensor signal wire at the ECM. Wiggle the harness during measurement to reveal an intermittent open condition. The resistance should be less than 5 ohms. If the resistance is greater than 5 volts, there is an open circuit in the wire. Replace the wire and retest.

  6. 6

    Reconnect the throttle position sensor to the engine harness. Remove the signal wire from the ECM connector with a wire removal tool. Set a digital voltmeter to measure voltage. Place the positive probe on the signal wire and place the negative probe on ground. Vary the position of the throttle sensor. The voltage should vary from 0.5 volts to 4.5 volts. If the voltage is not correct, there is a problem with the throttle sensor. Replace the sensor and retest. If the voltage is correct, there may be a problem with the ECM. Take the vehicle to a qualified mechanic for testing and repair.

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