S70 L5-2.4L VIN 61 B5244S (2000)
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°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. 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. The rear short-term fuel trim takes longer to warm up. This is to prevent damage to the probe. 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°C. The
probes maintain this as a minimum temperature.
The engine control module (ECM) can diagnose the heater element.
