Subaru LEGACY 2002 - System Overview

Emission Control (Aux. Emission Control Devices)
SYSTEM OVERVIEW
EC-2
1. System Overview
There are three emission control systems which are as follows:
! Crankcase emission control system
! Exhaust emission control system
! Three-way catalyst system
! Air/fuel (A/F) control system
! Ignition control system
! Evaporative emission control system
Item Main components Function
Crankcase emission control
system
Positive crankcase ventilation
(PCV) valve
Draws blow-by gas into intake manifold from crankcase and
burns it together with air-fuel mixture. Amount of blow-by gas to
be drawn in is controlled by intake manifold pressure.
Exhaust
emis-
sion
control
system
Catalyst
system
Front Three-way catalyst Oxidizes HC and CO contained in exhaust gases as well as re-
ducing NOx.
Rear
A/F control
system
Engine control module (ECM) Receives input signals from various sensors, compares signals
with stored data, and emits a signal for optimal control of air-
fuel mixture ratio.
Front oxygen (A/F) sensor Detects quantity of oxygen contained exhaust gases.
Rear oxygen sensor Detects density of oxygen contained exhaust gases.
Throttle position sensor Detects throttle position.
Intake air temperature and
pressure sensor
Detects absolute pressure of intake manifold.
Detects intake air temperature of intake manifold.
Ignition control
system
ECM Receives various signals, compares signals with basic data
stored in memory, and emits a signal for optimal control of igni-
tion timing.
Crankshaft position sensor Detects engine speed (Revolution).
Camshaft position sensor Detects reference signal for combustion cylinder discrimina-
tion.
Engine coolant temperature
sensor
Detects coolant temperature.
Knock sensor Detects engine knocking.
Evaporative emission control
system
Canister Absorbs evaporative gas which occurs in fuel tank when engine
stops, and releases it to combustion chambers for a complete
burn when engine is started. This prevents HC from being dis-
charged into atmosphere.
Purge control solenoid valve Receives a signal from ECM and controls purge of evaporative
gas absorbed by canister.