Introduction to On Board Diagnostics (II)

Functionality of PowertrainControl Module (PCM) inOBD II DiagnosticsPerform powertrain control functions to reduce emissionsand meet OBD II regulations.Secondary Air management (contd): The converter can be damaged if too muchheat is applied to it. This can occur if large amounts of HC and CO are oxidized inexhaust manifold during heavy loads which call for fuel enrichment or duringsevere deceleration. In such cases, the PCM directs the secondary air to the aircleaner where it has no effect on exhaust temperature.After warm-up, the main use of secondary air is to provide an oxygen rich air to thesecond chamber of the three-way catalyst, dual-chamber converter system. In thedual chamber converter, the first chamber contains rhodium, and platinum toreduce NOx and to oxidize HC and CO. The second chamber contains only platinumand palladium.. The extra oxygen from the secondary air improves the ability of theconverter to oxidize the HC and CO in the second converter chamber. The PCMcontrols the secondary air using two solenoid valves similar to EGR valve.