Catalytic Converter System

Catalytic Converter System

Heated oxygen sensor The heated oxygen sensor (HO2S) is part of a closed loop-type exhaust emission system. The sensor is fitted in the exhaust manifold and is designed to monitor the exhaust gases. In weak air/fuel mixtures, oxygen content in the exhaust gas increases, decreasing the voltage output to the ECM. As the air/fuel mixture becomes richer so oxygen content decreases, increasing the voltage output to the ECM.

One side of the oxygen sensor relay coil receives an earth from the ECM on the B wire providing the starter switch is in position II. The other side of the relay coil receives battery voltage from link 4 in the engine compartment fuse box on the N wire via the contacts of the main relay (providing it is energised). As a result battery voltage is switched from link 4 in the engine compartment fuse box on the N wire via the closed contacts of the oxygen sensor relay to the oxygen sensor on the U/R-W wire. Since an earth is provided on the B-W wire, the integral heating element will quickly reach an efficient operating temperature from cold.

The resultant output voltage on the LG/S and S wires is used by the ECM to determine what correction to fuel delivery is necessary.

CAUTION: An oxygen sensor will not operate if its power supply is removed, if it has been dropped, subjected to any impact or if cleaning materials are used on it.

Purge Valve

The purge valve receives battery voltage on the N/K wire from link 4 in the engine compartment fuse box on the N wire via the contacts of the main relay (providing it is energised) and a control signal from the ECM on the B/W wire. The valve remains closed when the engine is cold and at idling speed to protect engine tune and catalyst performance. When the coolant is above 70oC, the purge valve solenoid will be modulated ON and OFF whenever the engine speed is above 1500 rev/min and the manifold absolute pressure is below 30kpa. When the purge valve is open, fuel vapour from the charcoal canister is drawn into the throttle housing for combustion.