GM Cavalier/Sunbird/Skyhawk/Firenza 1982-1994

Manifold Absolute Pressure (MAP) Sensor

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OPERATION



See Figure 1

The Manifold Absolute Pressure (MAP) sensor measures the changes in intake manifold pressure, which result from engine load and speed changes and converts this information to a voltage output. The MAP sensor reading is the opposite of a vacuum gauge reading: when manifold pressure is high, MAP sensor value is high and vacuum is low. A MAP sensor will produce a low output on engine coastdown with a closed throttle while a wide open throttle will produce a high output. The high output is produced because the pressure inside the manifold is the same as outside the manifold, so 100% of the outside air pressure is measured.

The MAP sensor is also used to measure barometric pressure under certain conditions, which allows the ECM to automatically adjust for different altitudes.



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Fig. Fig. 1: MAP sensor

The MAP sensor changes the 5 volt signal supplied by the computer control module (ECM or PCM as applicable), which reads the change and uses the information to control fuel delivery and ignition timing.

TESTING



The test requires the use of a scan tool.

  1. If the engine idle is rough, unstable or incorrect, fix before using this test.
  2.  
  3. With the engine idling, hook up a scan tool. If the scan tool does not display a MAP of 4.0 or more volts, the trouble code is intermittent. Check all connections and make sure the sensor is mounted securely.
  4.  
  5. If the MAP is over 4.0 volts, turn the ignition OFF , then detach the MAP sensor connector and turn the ignition to the ON position. The scan tool should read a voltage of 1 volt or less.
    1. If the voltage reading is 1 volt or less, probe CKT 455 with a test light to 12 volts. If the test light lights, the MAP sensor hose is plugged or leaking, or the MAP sensor is faulty. If the test light doesn't light, CKT 455 is open.
    2.  
    3. If the voltage reading is more than 1 volt, CKT 432 is shorted to voltage, shorted to CKT 474 or the ECM/PCM is faulty.
    4.  

  6.  

REMOVAL & INSTALLATION



See Figures 2 and 3

  1. Disconnect the negative battery cable.
  2.  
  3. If necessary, unfasten the retainer clip from the engine bracket assembly-to-MAP sensor assembly.
  4.  
  5. Disconnect the vacuum line, then detach the electrical connector from the MAP sensor.
  6.  
  7. Remove the MAP sensor from the vehicle.
  8.  



Click image to see an enlarged view

Fig. Fig. 2: Be careful not to break the connector locktab



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Fig. Fig. 3: MAP sensor mounting - 3.1L engine shown

To install:
  1. Attach the vacuum line and the electrical connector to the MAP sensor.
  2.  
  3. Fasten the MAP sensor assembly to the engine bracket.
  4.  
  5. Install the retaining clip.
  6.  
  7. Connect the negative battery cable.
  8.  

 
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