Front Heated Oxygen Sensor (Ho2S) Function; Front Heated Oxygen Sensor (Ho2S) Construction/Operation - Mazda RX-8 2004 Service Highlights

• Built into the intake air temperature IAT sensor.
• Converts the mass intake airflow amount into a
voltage.
• When the heating element is placed in the air, the
heat is dissipated by the air cooling the heating
element. If there is a large volume of air
circulating around the heating element, the
amount of heat that is dissipated increases. This
heat transfer utilizes the voltage which is changed
by the heat transfer phenomenon.
AIR THERMOMETER
CONTROL CIRCUIT
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FRONT HEATED OXYGEN SENSOR (HO2S) FUNCTION

• The wide-range air/fuel ratio sensor, which can linearly detect the oxygen concentration (air/fuel ratio of the air-
fuel mixture) in the exhaust gas in all ranges, from lean to rich, is used on the front HO2S.
• A heater has been adopted on the front HO2S, allowing stable detection of the oxygen concentration even
when the exhaust gas temperature is low.
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FRONT HEATED OXYGEN SENSOR (HO2S) CONSTRUCTION/OPERATION

• Installed on the exhaust manifold.
• The wide-range air/fuel ratio sensor is a pump cell
type sensor, using both the oxygen concentration
cell action and oxygen pump cell action, and can
detect the oxygen concentration (air/fuel ratio of
the air-fuel mixture) in the exhaust gas in all
ranges, from lean to rich.
• A heater is built into the sensor to facilitate the
activation of the HO2S at engine startup (when
the exhaust gas temperature is low).
Operation
• The wide-range air/fuel ratio sensor converts the
oxygen concentration in the exhaust gas into a
current value, and sends the value to the PCM.
• The PCM calculates the λ (lambda) value of the
air-fuel mixture based on the received current
value.
• (λ (lambda)) = (actual air/fuel ratio)/
(stoichiometric air/fuel ratio)
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01–40–50
CONTROL SYSTEM
B+
MAF SENSOR
VOLTAGE
HOT WIRE
CURRENT
INTAKE AIR
MAF SENSOR
OUTPUT VOLTAGE CHARACTERISTIC
PCM
HIGH
CPU
LOW
LOW
INTAKE AIR AMOUNT
FRONT HO2S
1
0.5
0
-0.5
-1
-1.5
1
0.7 0.9
0.8
14.7 16.17 17.64 19.11 20.58
10.29 13.23
11.76
AIR THERMOMETER
HOT WIRE
CHU0140S080
HIGH
CHU0140S081
CHU014018860S01
CHU014018860S02
CHU0140S061
1.1 1.4 (λ)
1.2 1.3
(A/F)
CHU0140S074