How to test engine sensors

Written by dan swords
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How to test engine sensors
Test the sensors on your car for maximum performance. (Jupiterimages/Comstock/Getty Images)

Car engines are being controlled more and more by electronics. The mechanical governor of the past has been replaced by the electronic control module and sensors. These components work together to improve engine performance and to reduce harmful emissions. The electronic control module monitors these sensor signals and can diagnose when a sensor has failed. The electronic control module will display a specific diagnostic code for that sensor. These codes can be retrieved with the use of a diagnostic tool. Once the code has been retrieved, test the sensor to determine if the sensor has actually failed.

Skill level:
Moderate

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Things you need

  • Digital volt meter
  • Basic hand tools
  • Baking soda
  • Small wire brush or old toothbrush
  • Electrical tape
  • Wire removal tool
  • Electrical schematic and engine manual for your engine

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Instructions

    Engine Harness and Connection Testing

  1. 1

    Turn off the key switch and open the bonnet. Verify that the battery is free of corrosion, dirt and debris. If corrosion is found on the battery terminal, use baking soda and a small wire brush to remove the corrosion.

  2. 2

    Inspect the engine harness to verify that it is free of corrosion, abrasion and damage. If damage is found, use electrical tape to temporarily repair the harness. Replace the harness if needed.

  3. 3

    Inspect all of the electrical connections. Verify that the connection to the electronic control module and sensor is tight and secure.

    Pressure Sensor Testing

  1. 1

    Turn off the key switch. Disconnect the suspect pressure sensor from the engine harness. Remove the sensor from the pressure port.

  2. 2

    Refer to the engine electrical schematic and remove the signal wire from the sensor electrical connector. Reconnect the sensor to the engine harness.

  3. 3

    Turn on the key switch. Use the digital volt meter to measure the sensor output. Place the positive probe on the signal wire and place the negative probe on a clean chassis ground.

  4. 4

    Refer to the engine schematic or engine manual to verify the sensor pressure range. Gradually apply a pressure to the sensor while monitoring the sensor output voltage. The voltage should change from approximately 0.5 volts, to 4.5 volts.

    Temperature Sensor Testing

  1. 1

    Turn off the key switch. Disconnect the temperature sensor from the engine harness. Remove the sensor from the engine port.

  2. 2

    Refer to the engine electrical schematic and remove the signal wire from the sensor electrical connector. Reconnect the sensor to the engine harness.

  3. 3

    Turn on the key switch. Measure the sensor output with the digital volt meter. Place the positive probe on the signal wire and place the negative probe on a clean chassis ground.

  4. 4

    Gradually apply heat to the sensor while monitoring the sensor output voltage. The voltage should change from about 0.5 volts, to 4.5 volts.

    Throttle Position Sensor Testing

  1. 1

    Turn off the key switch. Disconnect the throttle sensor from the engine harness. Leave the sensor connected to the throttle assembly.

  2. 2

    Refer to the engine electrical schematic and remove the signal wire from the sensor electrical connector. Reconnect the sensor to the engine harness.

  3. 3

    Turn on the key switch. Measure the sensor output with the digital volt meter. Place the positive probe on the signal wire and place the negative probe on a clean chassis ground.

  4. 4

    Move the throttle while monitoring the sensor output. The voltage should change from about 0.5 volts at low idle to 4.5 volts at full throttle.

Tips and warnings

  • When working around the battery, always disconnect the negative battery cable from the battery.
  • Many auto parts stores have the diagnostic equipment needed to retrieve the electronic control module diagnostic codes.
  • To test two wire temperature sensors, measure the resistance across the sensor while applying heat to the tip. The resistance should change as the sensor heats up.

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