XC70 L5-2.5L Turbo VIN 59 B5254T2 (2003)
Oxygen Sensor: Description and Operation
Heated Oxygen Sensors (HO2S)
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5 cylinder engines have two heated oxygen sensors (HO2S), front and rear
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6 cylinder engines have four heated oxygen sensors (HO2S), front and rear for bank 1 (cylinders 1-3) and front and rear for bank 2 (cylinders 4-6)
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XC90s with 6 cylinder engines utilize the Y-concept, where the engine has two heated oxygen sensors (HO2S) bank 1 (cyl. 1-3), bank 2 (cyl. 4-6)
and a rear heated oxygen sensor (HO2S) (bank 1).
Front heated oxygen sensor (HO2S)
The front heated oxygen sensor (HO2S) is used to provide the Engine Control Module (ECM) with information about the remaining oxygen content of
the exhaust gases in front of the three-way catalytic converter (TWC). This is so that the Engine Control Module (ECM) can continually check the
combustion so that lambda=1. Lambda=1 is the ideal fuel-air ratio, with 14.7 kg air/1 kg fuel.
The heated oxygen sensor (HO2S) uses current regulation and its signal characteristic is linear. With a linear signal characteristic, the amplitude of the
signal curve is low when changing the oxygen content in the exhaust gases. The probe consists of a preheating element (see "Pre-heating heated oxygen
sensors (HO2S)") and the actual lambda sensor. The lambda sensor is an oxygen sensitive ceramic body consisting of zirconium oxide. The control
module supplies power to the ceramic body, which reacts to the oxygen content of the exhaust gases. This in turn affects the signal to the engine control
module (ECM). In order to determine the oxygen content in the exhaust pipe, the heated oxygen sensor (HO2S) needs reference air from the surrounding
air. This reference air reaches the heated oxygen sensor (HO2S) via the wiring.
CAUTION: The wiring for the heated oxygen sensors (HO2S) must not be trapped or damaged in any way. The connectors for the heated oxygen
sensors (HO2S) must not be greased under any circumstances. The oil in the grease would disrupt the reference air and the function of the heated oxygen
sensors (HO2S).
The engine control module (ECM) can diagnose the heated oxygen sensor (HO2S). For further information, see Heated oxygen sensor (HO2S)
diagnostic. VADIS/VIDA can be used to read off the calculated lambda value from the heated oxygen sensor (HO2S).
Rear heated oxygen sensor (HO2S)
The rear heated oxygen sensor (HO2S) is used to provide the Engine Control Module (ECM) with information about the remaining oxygen content of the
exhaust gases beyond the three-way catalytic converter (TWC). This information is used by the Engine Control Module (ECM) to check the function of
the three-way catalytic converter (TWC). This check is carried out when the conditions for the catalytic converter diagnostics have been met. The rear
heated oxygen sensor (HO2S) has no direct effect on regulation of the fuel/air mixture. However the Engine Control Module (ECM) uses the signal to
optimize the signal from the front heated oxygen sensor (HO2S). For further information, see:
