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 a BG 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 an N wire via the contacts of the main relay (providing it is energised). As a result the oxygen sensor relay energises and battery voltage is switched from link 4 in the engine compartment fuse box on an N wire via the closed contacts of the oxygen sensor relay to the oxygen sensor on a UR wire. Since an earth is provided on a B wire, the integral heating element will quickly reach an efficient operating temperature from cold.

The resultant output voltage on the LGS 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 an NK wire from link 4 in the engine compartment fuse box on an N wire from the closed contacts of the main relay (providing it is energised) and a control signal from the ECM on a BW wire. The valve remains closed when the engine is cold and at idling speed to protect engine tune and catalyst performance. When the purge valve is open, fuel vapour from the charcoal canister is drawn into the throttle housing for combustion.

Automatic gearbox

Inhibitor switch The switch fitted to the gearbox inhibits operation of the starter motor unless the selector lever is in position P or N.

With the selector lever in position P or N the inhibitor switch will provide an earth path for the starter relay on a BLG wire which will allow the engine to be started.

If the selector lever is in any other position than P or N, the inhibitor switch will not provide an earth path, so preventing the vehicle starting.

The inhibitor switch also provides the ECM with an input so that idle speed is automatically adjusted when a drive position is selected.