FREE REPAIR MANUALS & LABOR GUIDES 1982-2013 Vehicles
Courtesy of Operation CHARM: Car repair manuals for everyone.
Home >> Volvo >> 2002 >> V70 2.4T AWD L5-2.4L Turbo VIN 58 B5244T3 >> Repair and Diagnosis >> Powertrain Management >> Computers and Control Systems >> Sensors and Switches - Computers and Control Systems >> Oxygen Sensor >> Description and Operation

Oxygen Sensor: Description and Operation




Heated Oxygen Sensors (HO2S)
- 5 cylinder engines have two heated oxygen sensors (HO2S), front and rear
- 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)
- 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 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).

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 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 rear heated oxygen sensor (HO2S). The signal can be read using VADIS.

Preheating of the heated oxygen sensors (HO2S)
The heated oxygen sensor (HO2S) only functions above a certain temperature, approximately 300 degree C. The normal operating temperature is between 300-900 degree C. The heated oxygen sensors (HO2S) are electrically pre-heated so that operating temperature is rapidly reached. This also ensures 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 the front heated oxygen sensor (HO2S) is short, approximately 20 seconds.

Probe preheating begins as soon as the engine is started. The heater element heats the heated oxygen sensors (HO2S) to approximately 350 degree C. The probes maintain this as a minimum temperature.

The engine control module (ECM) can diagnose the heater element.
pro multis Credits:Operation CHARM About Operation CHARM