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GM Corsica/Beretta 1988-1996 Repair Guide

Manifold Absolute Pressure (MAP) Sensor

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OPERATION



See Figure 1

The MAP sensor measures the changes in intake manifold pressure, which result from engine load/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 coast-down 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 percent of the outside air pressure is measured.



Click image to see an enlarged view

Fig. Fig. 1: Typical MAP sensor and electrical connector

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

The MAP sensor changes the 5 volt signal supplied by the PCM, which reads the change and uses the information to control fuel delivery and ignition timing.

TESTING



Except 1996 2.2L Engines and 1994-96 3.1L Engines

See Figures 2 and 3

  1. Visually check the connector, making sure it is connected properly and all of the terminals are straight, tight and free of corrosion.
  2.  
  3. Check the vacuum hose connected to the MAP sensor. Replace the hose if it is in bad condition, plugged or leaking.
  4.  
  5. Detach the electrical connector from the MAP sensor.
  6.  
  7. Turn the ignition switch to the ON position with the engine OFF .
  8.  
  9. Connect a voltmeter to a known good ground and terminal C of the harness:
    1. If there is 4.5-5.5 volts, proceed to the next step.
    2.  
    3. If the voltage is below 4.5 volts or above 5.5 volts, check the MAP sensor reference circuit.
    4.  

  10.  
  11. With he voltmeter connected to terminal C, connect the other voltmeter lead to terminal A.
    1. If there is 4.5-5.5 volts, proceed to the next step.
    2.  
    3. If the voltage is below 4.5 volts or above 5.5 volts, check the MAP sensor ground circuit.

      Click image to see an enlarged view

      Fig. Fig. 2: MAP sensor electrical circuit - 2.2L engines through 1995



      Click image to see an enlarged view

      Fig. Fig. 3: MAP sensor electrical circuit - 2.3L engine

    4.  

  12.  
  13. Turn the ignition switch to the OFF position.
  14.  
  15. Attach the electrical connector to the MAP sensor.
  16.  
  17. Remove the vacuum hose from the MAP sensor and connect a hand operated vacuum pump to the MAP sensor.
  18.  
  19. Use a voltmeter to backprobe the connector terminals A and B.
  20.  
  21. Turn the ignition switch to the ON position and check the voltage at terminals A and B:
    1. If the voltage is 4.0-4.8 volts, proceed to the next step.
    2.  
    3. If the voltage is below 4.0 volts or above 4.8 volts, replace the MAP sensor.
    4.  

  22.  
  23. Observe the voltage measurement while slowly applying 10 inches of vacuum as indicated on the pump gauge. The value should change smoothly and drop 1.5-2.1 volts:
    1. If the MAP sensor voltage drops 1.5-2.1 volts, the sensor is operating properly. Check the vacuum source.
    2.  
    3. If the MAP sensor voltage drops less than 1.5 volts or more than 2.1 volts, replace the MAP sensor.
    4.  

  24.  

1996 2.2L Engines and 1994-96 3.1L Engines

See Figures 4 and 5

  1. Visually check the connector, making sure it is connected properly and all of the terminals are straight, tight and free of corrosion.
  2.  
  3. With the ignition ON , check the voltage between terminals A and B. It should be above 4 volts. Apply 15 in. Hg of vacuum at the MAP vacuum port and check the voltage again. The voltage should be 2 volts now.
  4.  



Click image to see an enlarged view

Fig. Fig. 4: Manifold Absolute Pressure (MAP) sensor circuit

When pumping up and releasing the vacuum, check to make sure the voltage readings are smooth. When applying vacuum to the sensor, the change in voltage should happen instantly. A slow change in voltage could point to a faulty sensor.



Click image to see an enlarged view

Fig. Fig. 5: MAP sensor voltage specifications

  1. If the sensor voltage is not within specification, check for a 5 volt reference at terminal C. If the reference signal is found, the sensor is faulty.
  2.  
  3. If the sensor and circuits are functional, the PCM may be faulty.
  4.  

REMOVAL & INSTALLATION



See Figures 6 and 7

  1. Disconnect the negative battery cable.
  2.  
  3. Detach the MAP sensor electrical connector. Unplug the vacuum hose.
  4.  
  5. Unfasten the retaining screws/bolts, then remove the MAP sensor from the vehicle.
  6.  



Click image to see an enlarged view

Fig. Fig. 6: On the 2.2L engine, the MAP is secured with a retaining bolt



Click image to see an enlarged view

Fig. Fig. 7: Exploded view of the MAP sensor - 2.3L engines

To install:

If equipped, lightly coat the seal on the MAP sensor with clean engine oil.

  1. Attach the sensor electrical connector.
  2.  
  3. Connect the negative battery cable.
  4.  

 
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