Nissan 240SX/Altima 1993-1998 Repair Guide

Mass Air Flow Sensor

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OPERATION



The Mass Air Flow (MAF) sensor directly measures the amount of air flowing into the engine. The sensor is mounted between the air cleaner assembly and the air cleaner outlet tube.

The sensor utilizes a hot wire sensing element to measure the amount of air entering the engine. The sensor does this by sending a signal, generated by the sensor when the incoming air cools the hot wire, to the ECM. The signal is used by the ECM to calculate the injector pulse width, which controls the air/fuel ratio in the engine.

TESTING



See Figures 1, 2, 3, 4 and 5



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Fig. Fig. 1: The MAF sensor is attached to the air cleaner housing



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Fig. Fig. 2: To backprobe the MAF sensor connector, first remove the rubber boot



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Fig. Fig. 3: For this vehicle, the MAF voltage should be approximately 0.2 volts with the ignition ON. This sensor is within specifications



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Fig. Fig. 4: With the engine running at operating temperature, MAF voltage should be 0.85-1.35 volts. This sensor's reading is at the high side of the specification



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Fig. Fig. 5: Measure voltage by backprobing the MAF connector as illustrated

  1. Using a multimeter, check for voltage by backprobing the MAF sensor connector, as illustrated.
  2.  
  3. With the ignition switch ON and the engine stopped, voltage should be less than 1.0 volt.
  4.  
  5. With the engine idling at operating temperature, voltage should be 1.3 -1.7 volts.
  6.  
  7. With the engine running at approximately 4000 rpm, voltage should be approximately 4.0 volts.
  8.  

It is important to watch for a linear voltage rise in response to increases in engine rpm, up to about 4000 rpm.

  1. If voltage is not within specifications, check the power and ground circuits.
  2.  
  3. If the power and ground circuits test okay, the MAF sensor may be faulty.
  4.  

REMOVAL & INSTALLATION



  1. Loosen the hose clamps securing the air tube.
  2.  
  3. Disconnect the air tube from the MAF sensor and throttle body.
  4.  
  5. Label and disconnect the MAF sensor electrical harness.
  6.  
  7. Remove the MAF sensor attaching bolts.
  8.  
  9. Carefully remove the MAF sensor from the air box.
  10.  

To install:
  1. Position the MAF sensor in the air box.
  2.  
  3. Install the MAF sensor attaching bolts and tighten to 13-16 ft. lbs. (18-22 Nm).
  4.  
  5. Connect the MAF sensor's electrical harness.
  6.  
  7. Connect the air tube to the MAF sensor and throttle body.
  8.  
  9. Tighten the hose clamps securing the air tube.
  10.  

 
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