How to Test a MAP Sensor Without a Vacuum

Written by david mcguffin
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If you have noticed that your vehicle is backfiring or has lost power, then one or more of your sensors may be faulty. There are a variety of sensors that are utilised by the vehicle's engine control unit for proper timing and fuel mixture. The manifold absolute pressure sensor monitors the vacuum in the intake manifold.

Skill level:
Moderately Challenging

Things you need

  • OBD II scanner
  • Gaffer's tape
  • Multimeter

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  1. 1

    Use an OBD II scanner on your vehicle if you notice the check engine light coming on. One indication of the MAP sensor failing is when the check engine light only comes on when the vehicle is accelerating or during times of higher load or stress in the engine. Another sign that your MAP sensor is bad is when the vehicle hesitates during acceleration. Find the OBD II port on your vehicle, which is typically behind a panel underneath the steering wheel. Turn on the OBD II scanner and turn the key to the ignition to the accessories position. Look up the OBD code using websites such as AutoZone or OBD Codes if your scanner does not tell you the diagnosis of the code. Replace the MAP sensor to see if the problem is with the sensor itself or another component.

  2. 2

    Check for vacuum leaks between the air filter box and the manifold. Any hoses that are leaking, cracked or corroded may be causing the check engine light for the MAP sensor to come on, even if the sensor itself is still working properly. Other vacuum related problems include a stuck EGR (exhaust gas recirculation) valve or PCV (positive crankcase ventilation) valve. If you can feel air leaking from any of the hoses, wrap it with gaffer's tape to see if the performance of the MAP sensor returns to normal.

  3. 3

    Use a multimeter to test the MAP sensor and its electrical connection. Some MAP sensors need testing with a voltmeter while others need the use of a tachometer. Make sure that you use the correct setting for your MAP sensor component. Touch the probes of the multimeter to the electrical connection leading to the MAP sensor to test for continuity with the accessories position turned on in the ignition switch. If you do not get the correct voltage (consult a wiring diagram) for your vehicle, then your electrical system has malfunctioned, causing the MAP sensor to fail.

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