Short description :
Heated oxygen sensor (HO2S) - Fig. 14
Function
Sometimes referred to as a Lambda sensor.
Fitted in the exhaust system upstream of the catalytic converter, where it can measure the exhaust gases evenly from all
cylinders.
Where necessary (e.g. on a V-engine with a dual exhaust system) two sensors may be fitted.
1. Protective cap with slots
2. Heating element
3. Sensor element
4. Electrical connections
Operation
The sensor reacts to the oxygen content of the exhaust gasses and uses the voltage generated (200-800 mV) to signal
the ECM to modify the mixture (air/fuel) ratio.
If the oxygen content is at the ideal value (Lambda = 1), the sensor signal voltage will be 500 mV.
If the mixture is too weak the voltage will be 200-450 mV (Lambda 1,10).
If it is too rich the voltage will be 550-800 mV (Lambda 0,96).
In practice the oxygen sensor continually signals the ECM to alter the fuelling by a small amount, to maintain the mixture
strength as near as possible (± 1%) to the theoretical ideal (stoichiometric) ratio of 14.7 parts air to 1 part fuel, which is the
optimum for the catalytic converter to work efficiently.
The sensor will not begin to operate until it has reached 482-572°C, but most now incorporate a heater element, whichenables the closed loop system to come into operation soon after a cold start.
