1991 Subaru XT Emission Control System Inspect Cost

The emission control system of the vehicle is a group of components from multiple systems that work together to reduce the harmful environmental effects of using internal combustion engines. This system focuses on reducing emissions by increasing the efficiency of the engine, reducing evaporation of fuel, and cleaning the bulk of pollutants from exhaust gases. In fact, most electronic components on an engine relate directly to emissions. When the check engine light comes on, it signals an emission related failure, and related components of the emissions system will be inspected while diagnosing the emissions system failure.

The emission control system begins with the evaporative emission control system (EVAP). This systems prevents fuel vapors from evaporation from escaping from the vehicle. Since fuel evaporative emissions are among the most damaging to our environment, this is perhaps one of the more important systems. As fuel evaporates, it is held in a container until it is released into the engine to be used as fuel. Next, electronic ignition systems have increased the efficiency of engines by regulating fuel and air ignition according to many variables. Once burned, air and fuel is released into the exhaust system, but when possible, unburned air and fuel will be cycled through the exhaust gas recirculation system, as the name implies, to be recirculated through the engine and reused. Finally, the exhaust system uses oxygen sensors to prevent a large amount of fuel from passing through the engine unburned, and catalytic converters to reduce the release of specific chemical byproducts of combustion. There are several other components at work, and several other advances in technology that have led to making our combustion engines more efficient. It should be understood that the main goal of the emissions system is primarily focused on increasing engine efficiency to prevent the emission of pollutants.

Any time there is an emissions fault the check engine light will be displayed. The purpose of the check engine light is to inform the driver that an emission related fault has been found, and that there are on-board diagnostic (OBD) trouble codes stored in the powertrain or engine control module. Additionally, since the emissions systems are so intertwined into engine control and transmission control systems, symptoms may include nearly any sort of drivability concerns. This may include harsh shifting, failure to shift, hesitation on acceleration, jerking, engine failure to start or run, loss of power, or any number of other drivability issues.