Toyota Previa 1991-1997 Repair Information

Mass Airflow Meter (MAF)

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OPERATION



See Figure 1

The Mass Airflow Meter (MAF) is only applicable to the 2TZ-FZE engines. The MAF uses a platinum hot wire. The hot wire air flow meter consists of a platinum hot wire, thermister and control circuit installed in a plastic housing. The hot wire air flow meter works on the principle that the hot wire and thermister are located in the intake air bypass of the housing detect any changes in the intake air temperature.



Click image to see an enlarged view

Fig. Fig. 1: Cutaway view of the thermister in the airflow meter

The hot wire is maintained at the set temperature controlling by the current flow though the hot wire. This current flow is then measured as the output voltage of the air flow meter.

TESTING



See Figures 2, 3 and 4

Testing can be done without removing the MAF meter from the vehicle.

  1. If necessary, remove the MAF meter from the vehicle.
  2.  
  3. Disconnect the wiring from the airflow meter.
  4.  
  5. Using an ohmmeter, measure the resistance between each terminal (THA and E2) as shown in the charts.
  6.  



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Fig. Fig. 2: Mass air flow meter terminal identification-2TZ-FZE engine

  1. If the resistance is not as specified, replace the air flow meter.
  2.  



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Fig. Fig. 3: Mass Airflow Meter resistance values-2TZ-FZE engine

  1. Inspect the meter operation. Connect the MAF meter wiring.
  2.  
  3. Connect a voltmeter to the positive (+) test probe to the VG and the negative (-) test probe to terminal E3.
  4.  



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Fig. Fig. 4: Attach the test probe terminals to the E3 (first pin) and VG (fourth pin) from the left of the MAF meter-2TZ-FZE engine

  1. Blow air into the meter and check that the voltage fluctuates.
  2.  
  3. If the operation is not as specified, replace the MAF meter.
  4.  

REMOVAL & INSTALLATION



See Figure 5

  1. Disconnect the negative battery cable. Wait at least 90 seconds before proceeding on models with an airbag.
  2.  


CAUTION
Some models covered by this guide may be equipped with a Supplemental Restraint System (SRS), which uses an air bag. Whenever working near any of the SRS components, such as the impact sensors, the air bag module, steering column and instrument panel, disable the SRS, as described in Chassis Electrical .

  1. Disconnect the air flow meter wiring harness from the unit.
  2.  



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Fig. Fig. 5: View of the Mass Airflow Meter and surrounding components-2TZ-FZE engine

  1. Disconnect the A/C idle-up valve wiring.
  2.  
  3. Separate the A/C idle-up air hoses form the valve.
  4.  
  5. Loosen the air cleaner hose clamp.
  6.  
  7. Loosen the 4 clips, and remove the air cleaner cap with MAF meter as an assembly off the engine.
  8.  
  9. Remove the MAF meter retaining bolts.
  10.  
  11. Installation is the reverse order of removal. Tighten the meter screws to 61 inch lbs. (7 Nm).
  12.  

 
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