Subaru 2002 Impreza Service Manual page 110

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SYSTEM OVERVIEW
Emission
Control
(Aux. Emission
Control Devices)
:rankcase emission control
system
1. System Overview
There are three emission control systems which are as follows:
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Crankcase emission control system
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Exhaust emission control system
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Three-way catalyst system
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Air/fuel (A/F) control system
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Ignition control system
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On-board refueling vapor recovery (ORVR) system
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Evaporative emission control system
Positive crankcase
ventilation (PCV)
valve
tern
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Main components
>atalyst
system
Pre Three-way catalyst
Front
Rear
Exhaust
mission
:ontrol
system
W F control
system
Function
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.
Engine control mod-
ule (ECM)
Evaporative emission control
system
3RVR system
Oxidizes HC and CO contained in exhaust gases as well as reducing
NOx.
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 discharged into
atmosphere.
Receives a signal from ECM and controls purge of evaporative gas
Controls evaporation pressure in fuel tank.
Closes the evaporation line by receiving a signal from ECM to check
the evaporation gas leak.
Purge control
solenoid valve absorbed by canister.
Vent valve
Drain valve
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 (NF)
sensor
Detects quantity of oxygen contained exhaust gases.
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Rear oxygen sensor
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Detects density of oxygen contained exhaust gases.
Throttle position
sensor
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Detects throttle position.
Mass air flow sensor
and intake air tem-
perature sensor
Detects amount of intake air.
Detects.intake air temperature of air cleaner case.
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ECM
gnition control
system
Receives various signals, compares signals with basic data stored in
memory, and emits a signal for optimal control of ignition timing.
Crankshaft position
sensor
Detects engine speed (Revolution).
Camshaft position
sensor
Detects reference signal for combustion cylinder discrimination.
Engine coolant tem-
perature sensor
Detects coolant temperature.
l % c k sensor
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Detects engine knocking
EC-2