Subaru 2002 IMPREZA Service Manual page 440

ENGINE (DIAGNOSTICS)
C: NOTE
1. DESCRIPTION
• The on-board diagnostics (OBD) system detects
and indicates a fault in various inputs and outputs
of the complex electronic control. CHECK ENGINE
malfunction indicator lamp (MIL) in the combination
meter indicates occurrence of a fault or trouble.
• Further, against such a failure or sensors as may
disable the drive, the fail-safe function is provided
to ensure the minimal driveability.
• The OBD system incorporated with the vehicles
within this engine family complies with Section
1968.1, California Code of Regulations (OBD-II
regulation). The OBD system monitors the compo-
nents and the system malfunction listed in Engine
Section which affects on emissions.
• When the system decides that a malfunction oc-
curs, MIL illuminates. At the same time of the MIL il-
lumination or blinking, a diagnostic trouble code
(DTC) and a freeze frame engine conditions are
stored into on-board computer.
• The OBD system stores freeze frame engine
condition data (engine load, engine coolant tem-
perature, fuel trim, engine speed and vehicle
speed, etc.) into on-board computer when it detects
a malfunction first.
• If the OBD system detects the various malfunc-
tions including the fault of fuel trim or misfire, the
OBD system first stores freeze frame engine condi-
tions about the fuel trim or misfire.
• When the malfunction does not occur again for
three consecutive driving cycles, MIL is turned off,
but DTC remains at on-board computer.
• The OBD-II system is capable of communication
with a general scan tool (OBD-II general scan tool)
formed by ISO 9141 CARB.
• The OBD-II diagnostics procedure is different
from the usual diagnostics procedure. When trou-
bleshooting OBD-II vehicles, connect Subaru Se-
lect Monitor or the OBD-II general scan tool to the
vehicle.
GENERAL DESCRIPTION
2. ENGINE AND EMISSION CONTROL SYS-
TEM
• The Multipoint Fuel Injection (MFI) system is a
system that supplies the optimum air-fuel mixture
to the engine for all the various operating condi-
tions through the use of the latest electronic tech-
nology.
With this system fuel, which is pressurized at a con-
stant pressure, is injected into the intake air pas-
sage of the cylinder head. The injection quantity of
fuel is controlled by an intermittent injection system
where the electro-magnetic injection valve (fuel in-
jector) opens only for a short period of time, de-
pending on the quantity of air required for one cycle
of operation. In actual operation, the injection quan-
tity is determined by the duration of an electric
pulse applied to the fuel injector and this permits
simple, yet highly precise metering of the fuel.
• Further, all the operating conditions of the engine
are converted into electric signals, and this results
in additional features of the system, such as large
improved adaptability, easier addition of compen-
sating element, etc.
The MFI system also has the following features:
3. AUTOMATIC TRANSMISSION AND
ELECTRONIC-HYDRAULIC CONTROL SYS-
TEM
The electronic-hydraulic control system consists of
various sensors and switches, a transmission con-
trol module (TCM) and the hydraulic controller in-
cluding solenoid valves. The system controls the
transmission proper including shift control, lock-up
control, overrunning clutch control, line pressure
control and shift timing control. It also controls the
AWD transfer clutch. In other words, the system
detects various operating conditions from various
input signals and sends output signals to shift sole-
noids 1, 2 and low clutch timing solenoid and 2-4
brake timing solenoid, line pressure duty solenoid,
lock-up duty solenoid, transfer duty solenoid and 2-
4 brake duty solenoid (a total of eight solenoids).
EN-8
• Reduced emission of harmful exhaust gases.
• Reduced in fuel consumption.
• Increased engine output.
• Superior acceleration and deceleration.
• Superior startability and warm-up perfor-
mance in cold weather since compensation is
made for coolant and intake air temperature.