How to Test a Pressure Sensor

by David McGuffin
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There are at least four different pressure sensors on modern automobiles, including those that measure the air intake pressure, atmospheric pressure and vapor pressure in your fuel tank. Modern vehicles use a variety of sensors, including those that measure pressure as well as other types that regulate the fuel-timing and ignition systems. If your vehicle is having pressure sensor issues, then you may be experiencing a wide variety of problems, including backfiring, reduction in horsepower or reduced ability to accelerate.

Step 1

Use an OBD II scanner to read troubleshoot codes from your car's ECM (engine control module), which can indicate specific sensors that are not working properly. The vehicle's OBD II terminal is usually located within two or three feet of the steering column, and is typically protected by a panel easily removed by hand. Plug the scanner into the terminal, turn on the scanner and turn the ignition key to the accessory position. If the scanner does not translate the OBD II codes, you will need to do this using a repair manual, or websites such as AutoZone, OBD Codes and others listed in the References section below.

Step 2

Test the parts related to the sensors that appear on the OBD scanner. For example, the MAP (manifold absolute pressure) sensor will not work correctly if you have a vacuum leak or air intake performance issue. For the MAP sensor, check the air intake assembly and all of its joints to make sure that air is able to pass through the assembly to the manifold. Also check all of the vacuum hoses for leaks or if they are displaced from their appropriate nozzles. If you detect a vacuum leak from any of the hoses or air intake, seal it with duct tape as a temporary fix.

Step 3

Use a multimeter or voltmeter to test the wiring and electrical connection leading to the sensors. Disconnect the electrical connection and touch the probes of the multimeter to the car's electrical harness. Turn on the engine and turn the multimeter to its voltage setting. Different sensors will have different voltage readings, however, if you do not detect any voltage coming from the vehicle's electrical system, then the wiring may need replacing. As an example, the MAP sensor should be receiving between 4.5 and 5.0 volts from the engine.

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