By-pass/Diverter Valve
Air from the air pump has three possible routes through the by-pass/diverter valve:
- Downstream air (air injected into three-way catalyst).
- Upstream air (air injected into exhaust manifold).
- By-pass (air by-passed to atmosphere).
The proper routing for thermactor air is determined by the ECA based on engine coolant temperature versus time curve and other sensor data. During normal coolant temperature operation the air is normally directed downstream. The air is by-passed when the closed throttle time exceeds a set time value, or if the time between the Exhaust Gas Oxygen lean/rich sensor exceeds a set time value. The air will also be by-passed during wide open throttle mode or during extended closed throttle operation.
During engine warm-up the thermactor air will be routed upstream. This is to help remove excessive amounts of HC and CO produced during the warm-up period.