Catalytic Converter System

Idle air control valve (stepper motor) The idle air control valve (IACV) is mounted on the inlet manifold. It receives battery voltage on an NK wire via the main contacts and is controlled by the ECM on OS (phase 1), KU (phase 2), OG (phase 3), and OU (phase 4) wires and receives an earth supply on a KB wire. During cold starting, the ECM provides a fast idle by sending a signal to the IACV which opens a pintle valve situated inside an air passage within the throttle housing. This allows air to bypass the throttle disc and flow directly into the inlet manifold. As the engine coolant temperature rises the fast idle is reduced until normal idle speed is attained.

Intake air temperature sensor The intake air temperature (IAT) sensor is located on the side of the inlet manifold. The IAT sensor is of the negative temperature coefficient (NTC) type, reducing its resistance with increases in air temperature. The ECM monitors the IAT sensor on a GB wire and is supplied with an earth on a B wire. When the ECM receives a signal from the sensor, it uses the signal along with that from the MAP sensor to calculate the volume of oxygen in the air and carry out fine adjustments of the injected fuel to attain the optimum mixture strength.

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.