RX300 1999

Air/Fuel Ratio Sensor

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Operation



Air-Fuel Ratio Sensor Heater

Specific to:

Lexus RX300 1999-2003

Lexus RX330 2004-2006

In order to achieve operating temperature and enter closed loop more quickly, modern oxygen sensors have built-in heating elements.

Component Description

Specific to:

Lexus RX300 1999-2003

Lexus RX330 2004-2006

The Air-Fuel Ratio (AFR) Sensor, also known as a Wideband Oxygen Sensor is a planar zirconia electronic device that measures the proportion of Hydrocarbons (HC) and oxygen (O2) content in the exhaust gas. The function of the AFR sensor is to constantly monitor the Air-Fuel ratio of the engine, determine if the mixture is rich or lean, and provide feedback (real-time information) to the Powertrain Control Module (PCM) so that the Air-Fuel ratio may be automatically adjusted.

Fuel Trim

Specific to:

Lexus RX300 1999-2003

Lexus RX330 2004-2006

Fuel trim is the PCM parameter that is used to adjust the Air-Fuel mixture. The ideal AFR Sensor feedback value is 2.5 volts DC, which is indicated when air and fuel are at the stoichiometric ratio of 14.7:1. This value is determined by AFR sensor feedback, and provides the final data for the PCM in determining the correct Air-Fuel mixture.

Removal & Installation



Specific to:

Lexus RX300 1999-2003

At this time the manufacturer does not provide removal and installation procedures for this component. The following procedure is a guideline and may differ from the vehicle you are servicing.

  1. Before servicing the vehicle, refer to the Precautions Section.
    NOTE
    If working near and/or around the SRS system and components, be sure to disable the SRS system.

  2.  
  3. Disconnect the negative battery cable.
    NOTE
    When disconnecting the cable be sure that the ignition switch and headlight switches are off.


    NOTE
    When disconnecting the cable, certain systems will have to be initialized after reconnecting the cable. These systems are adaptive front lighting system, power window control system, power back door system, SRS system, audio system, sliding roof system and certain DTC codes. Be sure to write down any important information before disconnecting the cable. The Toyota scan tool, or equivalent, must be used. Follow the directions on the appropriate scan tool to complete initialization procedure.

  4.  
  5. Raise and support the vehicle safely, as required.
  6.  
  7. Remove the components in order to gain access to the sensor.
  8.  
  9. Disconnect the sensor electrical connector.
  10.  
  11. Remove the sensor from its mounting.
    NOTE
    Do not drop the sensor. If the component is dropped, it must be replaced.

  12.  

To install:


NOTE
Be sure to use new fasteners, as required.

  1. Installation is the reverse of the removal procedure.
  2.  
  3. Before installing a new sensor coat the threads with an approved anti-seize lubricant.
  4.  

Testing



Specific to:

Lexus RX300 1999-2003

Lexus RX330 2004-2006


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

Air/Fuel Ratio Sensor

Specific to:

Lexus RX300 1999-2003

Lexus RX330 2004-2006

A properly operating heated Air-Fuel Ratio (AFR) sensor should display a level feedback signal of approximately 2.5 volts DC . If the feedback signal is not within the specified range, additional diagnosis is required in order to determine the proper function of the AFR sensor, or if a fault exists in any related sub-systems.

Air/Fuel Ratio Sensor Heater

Specific to:

Lexus RX300 1999-2003

Lexus RX330 2004-2006

The AFR sensor heater may be tested by performing a resistance test; the sensor must be disconnected from the main engine wiring harness. If the circuit resistance is greater than 5.0 ohms, replace the HO2S. Refer to the Electrical Wiring Diagram for specific circuit information and connector views.

Click image to see an enlarged view

Fig. Normal AFR sensor reading.

Air/Fuel Ratio Sensor Strategy

Specific to:

Lexus RX300 1999-2003

Lexus RX330 2004-2006

The AFR sensor operates most effectively when an operating temperature of 1,472° F (800° C) or higher is reached and maintained. When the AFR sensor reaches the specified temperature and begins sending the feedback signal, the PCM uses the information to enter closed loop mode, which is defined as the PCM having full control of the Air-Fuel ratio. In order to achieve operating temperature and enter closed loop more quickly, modern AFR sensors have built-in heating elements.

Connection & Wiring Diagnosis

Specific to:

Lexus RX300 1999-2003

Lexus RX330 2004-2006

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

Many intermittent open or short circuits may be caused by wiring harness and connector movement due to vibration, engine torque, bumps and rough pavement, etc.

  1. Test the wiring harness and connectors by performing the following tests:

    Move the related connectors and wiring while monitoring the appropriate scan tool data.
     
    Move the related connectors and wiring with the component commanded ON and OFF. Using a suitable the scan tool, observe the component operation.
     
    With the engine running, move the related connectors and wiring while monitoring component operation.
     
    If harness or connector movement affects the data displayed, the component and system operation, or the engine operation, inspect and repair the harness or connections as necessary.
     

  2.  
  3. Test the connector terminal pins and/or wiring by performing the following tests:

    Inspect for incorrect mating of the connector halves, or terminals not fully seated in the connector body.
     
    Inspect for improperly formed or damaged terminals and test for incorrect terminal tension.
     
    Inspect for poor terminal to wire connections including terminals crimped over insulation. This requires removing the terminal from the connector body.
     
    Inspect for corrosion or water intrusion. Pierced or damaged insulation can allow moisture to enter the wiring. The conductor can corrode inside the insulation with little visible evidence. Look for swollen and/or brittle sections of wire in the suspect circuits.
     
    Inspect for wires that are broken inside the insulation by gently pulling on suspect sections of wiring.
     

  4.  

Related Diagnostic Trouble Codes

Specific to:

Lexus RX300 1999-2003

Lexus RX330 2004-2006



Click image to see an enlarged view

Fig. Related Diagnostic Trouble Codes

 
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