ES300 1992-1997

Mass Air Flow Sensor (Hot Wire)

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Operation



Specific to:

Lexus ES250 1990-1991

Lexus ES300 1992-1999

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:

Lexus ES300 1992-1993

  1. Disconnect the negative battery cable.
  2.  
  3. Disconnect coil cord clamp.
  4.  
  5. Disconnect volume air flow meter connector.
  6.  
  7. Disconnect air cleaner hose.
  8.  
  9. Remove air cleaner cap and volume air flow meter assembly.
  10.  
  11. Remove volume air flow meter from air cleaner cap:
    1. Remove the screw and wire bracket.
    2.  
    3. Remove the bolt, two screws and bracket.
    4.  
    5. Pry off the lock plate, and remove the four nuts, lock plate, volume air flow meter and gasket.

      Click image to see an enlarged view

      Fig. Remove the volume air flow meter

    6.  

  12.  

To install:

  1. Install the volume air flow meter with the gasket, lock plate, four plate washers, four nuts and bolt. Install the lock plate on the nut.
  2.  
  3. Install the bracket with the bolt and two screws.
  4.  
  5. Install the wire bracket with the screw.
  6.  
  7. Install the air cleaner cap and volume air flow meter assembly.
  8.  
  9. Connect the air cleaner hose.
  10.  
  11. Connect the volume air flow meter connector.
  12.  
  13. Connect the coil cord clamp.
  14.  
  15. Connect the cable to negative terminal of battery.
  16.  

Specific to:

Lexus ES300 1994-1996

  1. Disconnect the negative battery cable.
  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 sensor-1994-96 models

  10.  

To install:

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

Specific to:

Lexus ES300 1997-1999

  1. Disconnect the negative battery cable.
  2.  
  3. Disconnect the MAF meter connector.
  4.  
  5. Remove the 2 bolts/screws, MAF meter and gasket/O-ring.

    Click image to see an enlarged view

    Fig. Remove the MAF sensor-1997-98 models



    Click image to see an enlarged view

    Fig. Remove the MAF sensor-1999 models

  6.  

To install:

  1. Installation is the reverse of removal. Install a new gasket/O-ring.
  2.  

Testing



Specific to:

Lexus ES250 1990-1991

Lexus ES300 1992-1999


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

MAF Circuit Testing

Specific to:

Lexus ES250 1990-1991

Lexus ES300 1992-1999

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:

Lexus ES250 1990-1991

Lexus ES300 1992-1999

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:

Lexus ES250 1990-1991

Lexus ES300 1992-1999



Click image to see an enlarged view

Fig. Related Diagnostic Trouble Codes

 
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