Rear Heated Oxygen Sensor (Ho2S) Function; Rear Heated Oxygen Sensor (Ho2S) Construction/Operation; Barometric Pressure (Baro) Sensor Function - Mazda RX-8 2004 Service Highlights

REAR HEATED OXYGEN SENSOR (HO2S) FUNCTION

• Detects the oxygen concentration in the exhaust gas.
• A heater has been adopted, allowing stable detection of the oxygen concentration even when the exhaust gas
temperature is low.
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REAR HEATED OXYGEN SENSOR (HO2S) CONSTRUCTION/OPERATION

• Installed on the catalytic converter.
• A heater is built into the sensor to facilitate the
activation of the HO2S at engine startup (when
the exhaust gas temperature is low).
• A zirconium element is used on the sensor. When
there is a difference between the oxygen
concentration inside and outside the element,
electromotive force is generated by the
movement of oxygen ions (inside of the zirconium
element: atmosphere, outside: exhaust gas). The
electromotive force changes significantly at the
boundary of the stoichiometric air/fuel ratio (A/
F=14.7). The PCM receives the voltage
generated from the HO2S directly, and increases
or decreases the fuel injection amount by the fuel injection control so that it is close to the stoichiometric air/fuel
ratio.
• When the temperature of the zirconium element is low, electromotive force is not generated. Therefore the
HO2S is heated by a built-in heater, facilitating the oxygen sensor activation. Due to this, the sensor is
efficiently activated even immediately after cold-engine startup, and a stable sensor output can be obtained.
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BAROMETRIC PRESSURE (BARO) SENSOR FUNCTION

• Detects the BARO.
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CONTROL SYSTEM
OUTPUT
VOLTAGE
REAR HO2S
HIGH
LOW
14.7
AIR/FUEL
RICH
RATIO
CHU014018860S03
CHU014018860S04
01–40
CHU0140S063
LEAN
CHU0140S075
CHU014018210S01
01–40–51