Avalon 1995-1996

Mass Air Flow Sensor (Hot Wire)

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Operation



Specific to:

Toyota Avalon 1995-1996

The Mass Air Flow (MAF) Sensor is a Positive Coefficient Thermistor (PTC) that determines the volume of air flowing into the intake system. The MAF Sensor operates within a 5 volt DC reference range, and provides a linear input signal to the Powertrain Control Module (PCM) that is based upon the measured engine intake air temperature. The thermistor, or -hot wire- is heated to a pre-determined temperature, and the then cools as the volume of air flowing past the wire increases. The PCM uses data from the MAF Sensor to calculate air-fuel mixture, ignition timing, and fuel injector pulse width. The MAF Sensor is sometimes integrated with the Intake Air Temperature (IAT) Sensor as a physical component.

Removal & Installation



Specific to:

Toyota Avalon 1995-1996

  1. Before servicing the vehicle, refer to the Precautions Section.
  2.  
  3. Disconnect the PCV hose.
  4.  
  5. Loosen the 2 hose clamps, and remove the air cleaner hose.
  6.  
  7. Disconnect the MAF meter connector.
  8.  
  9. Remove the 2 bolts and MAF meter.

    Click image to see an enlarged view

    Fig. Remove the MAF meter

  10.  

To install:

  1. Installation is the reverse order of removal. Tighten the meter screws to 61 inch lbs. (7 Nm).
  2.  

Testing



Specific to:

Toyota Avalon 1995-1996


NOTE
Refer to the Electrical Wiring Diagram for component and connector locations, connector views, and circuit-specific information.

MAF Circuit Testing

Specific to:

Toyota Avalon 1995-1996

Use a suitable scan tool, a Graphing Multi-Meter (GMM), or a Digital Volt-Ohm Meter (DVOM) in order to view the MAF data.

MAF Sensor logic is relative to the scale of resistance: when the intake air volume is low, the voltage is decreased. When the coolant temperature is high, the voltage is increased.

Inspect the air intake tube, the engine air filter, and the MAF and/or IAT sensors for contamination and physical damage in order to verify that the air induction system is in proper working order. If an air induction system fault is evident, repair as required before continuing.

If a DVOM is being used, additional information may be acquired by taking measurements at the sensor connector as well as the PCM connector. If a significant voltage drop is measured (greater than 0.5 volts DC), check the wiring harness and connections for corrosion, poor pin connections, or damaged wires.

If all engine wiring and pin connections are confirmed, disconnect the MAF Sensor to verify the signal with a DVOM, and verify PCM communication before replacing the MAF Sensor.

Click image to see an enlarged view

Fig. MAF Sensor Range Chart

MAF Sensor Strategy

Specific to:

Toyota Avalon 1995-1996

The MAF Sensor provides a linear input signal to the Powertrain Control Module (PCM) for a number of engine control system calculations. The MAF signal is compared with Manifold Absolute Pressure (MAP), Intake Air Temperature (IAT), Engine Coolant Temperature (ECT), and Fuel Trim (HO2S) in order to determine the correct air-fuel mixture for measured operating conditions.

Related Diagnostic Trouble Codes

Specific to:

Toyota Avalon 1995-1996



Click image to see an enlarged view

Fig. Related Diagnostic Trouble Codes

 
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