XC90 AWD V8-4.4L VIN 85 B8444S (2005)
The heated oxygen sensors (HO2S) can be diagnosed by the engine control module (ECM), and signals from them can be read off. For further
information: Heated oxygen sensor (HO2S) diagnostic See: Powertrain Management/Computers and Control Systems/Description and Operation/Heated
Oxygen Sensor (HO2S) Diagnostic
The control module can be used to read off the calculated lambda value from the heated oxygen sensor (HO2S) signal.
Rear heated oxygen sensor (HO2S)
Caution! The air lines 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 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: Three-way catalytic converter (TWC) diagnostics See:
Powertrain Management/Computers and Control Systems/Description and Operation/Three-Way Catalytic Converter (TWC) Diagnostics
The heated oxygen sensor (HO2S) uses voltage control. The signal characteristic is binary. With a binary signal characteristic, the amplitude of the
signal curve changes considerably when changing the oxygen content in the exhaust gases. Otherwise its components and function are the same as the
front heated oxygen sensor (HO2S).
Caution! The air lines 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).
There are two rear heated oxygen sensors; one for bank 1 and one for bank 2.
Bank 1 (front cylinder row); cylinders 1, 3, 5 and 7.
Bank 2 (rear cylinder row, closest to the passenger compartment); cylinders 2, 4, 6 and 8.
The heated oxygen sensors (HO2S) can be diagnosed by the engine control module (ECM), and signals from them can be read off
Preheating of the heated oxygen sensors (HO2S)
The heated oxygen sensor (HO2S) only functions above a certain temperature, approximately 300° C. The normal operating temperature is between
300-900° C. The heated oxygen sensors (HO2S) are electrically pre-heated so that operating temperature is rapidly reached. They are also pre-heated to
ensure that the heated oxygen sensors (HO2S) maintain a normal operating temperature and to prevent condensation which could damage the heated
oxygen sensor (HO2S).
The heater element in the probe consists of a positive temperature coefficient (PTC) resistor. The system relay supplies the heater element with voltage.
The element is grounded in the engine control module (ECM). When the control module grounds the connection a current flows through the PTC
resistor. When the heated oxygen sensor (HO2S) is cold, the resistance in the PTC resistor is low and a large current will flow through the circuit. The
current from the engine control module (ECM) is pulsed at first to prevent condensation damage to the heated oxygen sensor (HO2S). Depending on the
temperature, allowances are made for factors such as the dew point. As the temperature in the PTC resistor rises, the resistance rises, the current falls and
switches in stages to a constant current. The pre-heating time for front heated oxygen sensor (HO2S) is short, approximately 20 seconds.
The heater element heats the heated oxygen sensors (HO2S) to approximately 350 °C. The probes maintain this as a minimum temperature.
The engine control module (ECM) can diagnose the heater element.
Stop lamp switch
