Heated Oxygen Sensor (Ho2S) Construction/Operation [Lf]; Front Ho2S; Rear Ho2S - Mazda 2006 MX-5 Service Highlights

HEATED OXYGEN SENSOR (HO2S) CONSTRUCTION/OPERATION [LF]

• Installed on the front of the WU-TWC, and back of
the TWC.

Front HO2S

• The wide-range air/fuel ratio sensor is a limited current type sensor, 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).
• 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)/14.7

Rear HO2S

• 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.
End Of Sie
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CONTROL SYSTEM
REAR HO2S
1
0.5
0
-0.5
-1
-1.5
0.7
OUTPUT
VOLTAGE
1 1.1
0.9
0.8
HIGH
LOW
14.7
AIR/FUEL
RICH
RATIO
E5U014018860N02
FTONT HO2S
E5U140ZW5307
(λ)
1.3 1.4
1.2
E5U140ZN5851
LEAN
CHU0140S075