Heated oxygen sensor (HO2S)

Heated oxygen sensor (HO2S)

2 HO2S’s are fitted to the vehicle, 1 before each catalyst. A HO2S comprises a titanium metal sensor surrounded by a gas permeable ceramic coating. Oxygen permeating the ceramic coating reacts with the titanium wire, altering its resistance. The resistance of the sensor is directly related to the quantity of oxygen around the sensor. The HO2S does not function correctly until it reaches a temperature of approximately 300°C and so a heating element is incorporated into the sensor to provide rapid warm up after a cold start.

The signals from the HO2S’s are used by the ECM to correct the fuelling to each bank of cylinders independently. The 2 sensors measure the oxygen content of the gasses exhausted from the engine, indicating a rich or weak mixture strength. The ECM alters the pulse width of the injectors to correct the mixture strength and achieve a stoichiometric air/fuel ratio.

Injectors

The fuel injection system has 8 fuel injectors, 1 for each cylinder. Each injector comprises a solenoid with a needle valve held in position by a spring. The route to ground for the solenoid is controlled by the ECM. When energised, the solenoid lifts the needle valve from its seat and pressurised fuel from the fuel rail flows through the injector. The injector orifice is shaped to produce a fine spray of fuel which aids combustion.