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A/F (Bank1Sensor1) and HO2 (Bank1Sensor2) Sensors

Discussion in 'Engine' started by navylife59, Mar 9, 2010.

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  1. navylife59
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    navylife59 Super Moderator Staff Member

    Joined:
    Mar 22, 2006
    Location:
    Emory, Texas or Gretna, LA
    The A/F sensor generates a voltage* that corresponds to the actual air-fuel ratio. This sensor voltage is used to provide the ECM with feedback so that it can control the air-fuel ratio. The ECM determines the deviation from the stoichiometric air-fuel ratio level, and regulates the fuel injection time. If the A/F sensor malfunctions, the ECM is unable to control the air-fuel ratio accurately.

    The A/F sensor is the planar type and is integrated with the heater, which heats the solid electrolyte (zirconia element). This heater is controlled by the ECM. When the intake air volume is low (the exhaust gas temperature is low), a current flows into the heater to heat the sensor, in order to facilitate accurate
    oxygen concentration detection. In addition, the sensor and heater portions are narrower than the conventional type. The heat generated by the heater is conducted to the solid electrolyte through the alumina, therefore the sensor activation is accelerated.

    A three-way catalytic converter (TWC) is used in order to convert the carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxide (NOx) into less harmful substances. To allow the TWC to function effectively, it is necessary to keep the air-fuel of the engine near the stoichiometric air-fuel ratio. *: Value changes inside the ECM. Since the A/F sensor is the current output element, a current is
    converted to a voltage inside the ECM.

    Note: Any measurements taken at the A/F sensor or ECM connectors will show a constant voltage. That is why a piggyback controller or aftermarket A/FR gauge cannot be connected to read the OEM A/FR sensor values and the reason that regular OBDII/CAN scan tools cannot read the data either. The A/F sensor is a current output element; therefore, the current is converted into a voltage inside the ECM. The ECM regulates the voltage at the A1A+ and A1A- terminals of the ECM at a constant level. Therefore, the A/F sensor voltage output cannot be confirmed without using the Toyota Intelligent Tester.

    MONITOR DESCRIPTION
    Under the air-fuel ratio feedback control, if the A/F sensor voltage output indicates rich or lean for a certain period of time, the ECM determines that there is a malfunction in the A/F sensor. The ECM illuminates the MIL and sets a DTC.

    Example:
    If the A/F sensor voltage output is less than 2.8 V (very rich condition) for 10 seconds, despite the HO2 sensor voltage output being less than 0.85 V, the ECM sets DTC P2196. Alternatively, if the A/F sensor voltage output is more than 3.8V (very lean condition) for 10 seconds, despite the HO2 sensor voltage output being 0.15 V or more, DTC P2195 is set.

    MONITOR STRATEGY
    Related DTCs
    P2195: A/F sensor signal stuck lean
    P2196: A/F sensor signal stuck rich​
    Required Sensors/Components (Main)
    A/F sensor​
    Required Sensors/Components (Related)
    HO2 sensor​
    Frequency of Operation
    Continuous​
    Duration
    10 seconds: Sensor voltage detection monitor
    3 seconds: Sensor current detection monitor​
    MIL Operation
    2 driving cycles​
    Sequence of Operation
    None​

    AFR Bank1Sensor1 Schematic.jpg
     
  2. navylife59
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    navylife59 Super Moderator Staff Member

    Joined:
    Mar 22, 2006
    Location:
    Emory, Texas or Gretna, LA
    How To Check For Bad O2 Sensor



    1. INSPECT AIR FUEL RATIO SENSOR (for Bank1Sensor1)

    (a) Measure the resistance of the sensor.
    Standard resistance
    Bank1Sensor1 Measurement Test.jpg

    Tester Connection Specified Condition
    1 (HT) - 2 (+B) 1.8 to 3.4 Ω at 20°C (68°F)
    1 (HT) - 4 (AF-) 10 kΩ or higher

    Air/Fuel Ratio (A/FR) Bank1Sensor1 Circuit
    Bank1Sensor1Reference Diagram.jpg

    If the resistance is not as specified, replace the sensor.


    1. INSPECT HEATED OXYGEN SENSOR (for Bank1Sensor2)
    (a) Measure the resistance of the sensor.
    Standard resistance
    Bank1Sensor2 Measurement Test.jpg

    Tester Connection Specified Condition
    1 (HT) - 2 (+B) 11 to 16 Ω at 20°C (68°F)
    1 (HT) - 4 (E) 10 kΩ or higher

    Heated Oxygen Sensor (HO2) Bank1Sensor2 Circuit
    Bank1Sensor2 Reference Diagram.jpg

    If the resistance is not as specified, replace the sensor.

    Exploded View - Oxygen Sensor
    Bank1Sensor2 Exploded View.jpg
     
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