LaCrosse 2006-2007

Manifold Absolute Pressure Sensor

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Operation



The Manifold Absolute Pressure (MAP) sensor measures the pressure inside the intake manifold. Pressure in the intake manifold is affected by engine speed, throttle opening, air temperature, and Barometric Pressure (BARO). A diaphragm within the MAP sensor is displaced by the pressure changes that occur from the varying load and operating conditions of the engine. The sensor translates this action into electrical resistance. The MAP sensor wiring includes 3 circuits. The Engine Control Module (ECM) supplies a regulated 5 volts to the sensor on a 5 volt reference circuit. The ECM supplies a ground on a low reference circuit. The MAP sensor provides a signal voltage to the ECM, relative to the pressure changes, on the MAP sensor signal circuit. The ECM converts the signal voltage input to a pressure value.

Under normal operation the greatest pressure that can exist in the intake manifold is equal to BARO. This occurs when the vehicle is operated at Wide Open Throttle (WOT) or when the ignition is ON while the engine is OFF. Under these conditions, the ECM uses the MAP sensor to determine the current BARO. The least manifold pressure occurs when the vehicle is idling or decelerating. MAP can range from 10 kPa, when pressures are less, to as great as 104 kPa, depending on the current BARO. The ECM monitors the MAP sensor signal for pressure outside of the normal range.

Removal & Installation



3.8L Engine

The Manifold Absolute Pressure (MAP) sensor is mounted to the Positive Crankcase Ventilation (PCV) valve cover.

  1. Remove the fuel injector sight shield.
  2.  
  3. Disconnect the MAP sensor electrical connector.
  4.  
  5. Carefully release the locking tabs holding the MAP (1) sensor to the PCV valve cover (2) just enough to remove the MAP sensor.
  6.  
  7. Pull the MAP sensor straight out of PCV valve cover.

    Click image to see an enlarged view

    Fig. Manifold Absolute Pressure (MAP) sensor location-3.8L engine

  8.  

To install:

  1. Ensure that the seal is installed on the MAP sensor and that the seal is not damaged.
  2.  
  3. Position and install the MAP sensor (1) to the PCV valve cover (2). Ensure that the locking tabs engage to hold the MAP sensor to the PCV valve cover.
  4.  
  5. Connect the MAP sensor electrical connector.
  6.  
  7. Install the fuel injector sight shield.
  8.  

Testing



Poor idle characteristics may be due to uncontrolled fueling caused by an open or high resistance in the Heated Oxygen Sensor (HO2S) 1 low signal circuit. Before replacing any component, ensure that this condition does not exist.

  1. Start the engine.
  2.  
  3. Monitor the DTC information with the scan tool.
  4.  
  5. Turn the engine OFF.
  6.  
  7. If DTC P0641 or P0651 are set, correct these codes first.
  8.  
  9. Verify the integrity of the entire air induction system by inspecting for the following conditions:

    Any damage to, or hairline fractures of, the MAP sensor housing
     
    Disconnected, damaged, or incorrectly routed vacuum hoses
     
    Manifold Absolute Pressure (MAP)sensor disconnected from the vacuum source
     
    Restrictions in the MAP sensor vacuum source
     
    Intake manifold vacuum leaks
     
    Inspect for a properly functioning oxygen sensor
     

  10.  
  11. With the ignition ON, and the engine OFF, disconnect the MAP sensor.
  12.  
  13. Using a Digital Multi-Meter (DMM), measure the 5-volt reference circuit of the MAP sensor to a good ground. The reading should be 4.8-5.2 volts.
    1. If more than 5.2 volts, then test the circuit for a short to voltage. If the circuit tests normal, replace the control module.
    2.  
    3. If less than 4.8 volts, then test the circuit for high resistance, an open, a short to ground, or an intermittent or poor connection at the control module. If the circuit tests normal, replace the control module.

      Click image to see an enlarged view

      Fig. Manifold Absolute Pressure (MAP) connector end view-3.8L engine

    4.  

  14.  
  15. Use a scan tool and observe the MAP sensor. It should read less than 12 kPa.
    1. If the MAP sensor is more than 12 kPa, test the MAP sensor signal circuit for a short to voltage.
    2.  
    3. If the circuit tests normal, replace the control module.
    4.  

  16.  
  17. Use a 3-Amp fused jumper wire and connect it between the MAP sensor 5-volt reference circuit and the MAP sensor signal circuit.
  18.  
  19. Use a scan tool and observe the MAP sensor. It should read more than 103 kPa.
    1. If the MAP sensor is less than 103 kPa, test the MAP sensor signal circuit for a short to ground, an open, high resistance.
    2.  
    3. If the circuit tests normal, replace the control module.
    4.  

  20.  
  21. Turn OFF the ignition and allow the control module to power down.
  22.  
  23. Remove the MAP sensor from the engine vacuum source, but leave the MAP sensor connected to the engine harness.
  24.  
  25. Connect the J 23738-A, or a similar vacuum pump, to the MAP sensor.
  26.  
  27. Turn ON the ignition, with the engine OFF.
  28.  
  29. Observe the MAP sensor pressure with the scan tool.
  30.  
  31. Apply vacuum to the MAP sensor with the J 23738-A in 1 inch Hg increments until 15 inches Hg is reached. Each 1 inch Hg should decrease MAP sensor pressure by 3-4 kPa. Monitor the MAP sensor pressure to see if the decrease in pressure is consistent.
    1. If decrease in pressure is not consistent then, test for intermittent and poor connections at the MAP sensor.
    2.  
    3. If connections test OK, replace the MAP sensor.
    4.  

  32.  
  33. Apply vacuum with the J 23738-A until 20 inches Hg is reached. Observe the MAP sensor pressure. It should read less than 34 kPa.
    1. If the pressure is more than 34 kPa, test for an intermittent or poor connection at the MAP sensor.
    2.  
    3. If connections test OK, replace the MAP sensor.
    4.  

  34.  
  35. With a DMM, measure the resistance between the low reference circuit of the MAP sensor and battery negative post. It should read less than 5 ohms.
    1. If the resistance is more than 5 ohms, test the low reference circuit for a high resistance.
    2.  
    3. If the circuit tests normal, replace the control module.
    4.  

  36.  

 
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