Subaru Legacy III (2000-2003 year). Manual - part 301

EN(H6DO)-6

ENGINE (DIAGNOSTICS)

GENERAL DESCRIPTION

3. General Description

A: CAUTION

1) Airbag system wiring harness is routed near the
engine control module (ECM), main relay and fuel
pump relay.

CAUTION:
• All Airbag system wiring harness and con-
nectors are colored yellow. Do not use electri-
cal test equipment on these circuit.
• Be careful not to damage Airbag system wir-
ing harness when servicing the engine control
module (ECM), transmission control module
(TCM), main relay and fuel pump relay.
2) Never connect the battery in reverse polarity.
• The ECM will be destroyed instantly.
• The fuel injector and other part will be damaged
in just a few minutes more.
3) Do not disconnect the battery terminals while the
engine is running.
• A large counter electromotive force will be gener-
ated in the alternator, and this voltage may damage
electronic parts such as ECM, etc.
4) Before disconnecting the connectors of each
sensor and the ECM, be sure to turn OFF the igni-
tion switch.
5) Poor contact has been identified as a primary
cause of this problem. To measure the voltage and/
or resistance of individual sensors or all electrical
control modules at the harness side connector, use
a tapered pin with a diameter of less than 0.64 mm
(0.025 in). Do not insert the pin more than 5 mm
(0.20 in) into the part.
6) Before removing ECM from the located position,
disconnect two cables on battery.
• Otherwise, the ECM may be damaged.

CAUTION:
When replacing ECM, be careful not to use the
wrong spec. ECM to avoid any damage on fuel
injection system.
7) The connectors to each sensor in the engine
compartment and the harness connectors on the
engine side and body side are all designed to be
waterproof. However, it is still necessary to take
care not to allow water to get into the connectors
when washing the vehicle, or when servicing the
vehicle on a rainy day.

8) Use ECM mounting stud bolts at the body head
grounding point when measuring voltage and resis-
tance inside the passenger compartment.

9) Use engine grounding terminal or engine proper
as the grounding point to the body when measuring
voltage and resistance in the engine compartment.

10) Use TCM mounting stud bolts at the body head
grounding point when measuring voltage and resis-
tance inside the passenger compartment.

11) Every MFI-related part is a precision part. Do
not drop them.

(A) Stud bolt

(A) Stud bolt

EN-00001

( A )

EN-00752

EN-00790

( A )

EN(H6DO)-7

ENGINE (DIAGNOSTICS)

GENERAL DESCRIPTION

12) Observe the following cautions when installing
a radio in MFI equipped models.

CAUTION:
• The antenna must be kept as far apart as pos-
sible from the control unit.
(The ECM is located under the steering column,
inside of the instrument panel lower trim panel.)
• The antenna feeder must be placed as far
apart as possible from the ECM and MFI har-
ness.
• Carefully adjust the antenna for correct
matching.
• When mounting a large power type radio, pay
special attention to the three items above men-
tioned.
• Incorrect installation of the radio may affect
the operation of the ECM.
13) Before disconnecting the fuel hose, disconnect
the fuel pump connector and crank the engine for
more than five seconds to release pressure in the
fuel system. If engine starts during this operation,
run it until it stops.
14) Problems in the electronic-controlled automatic
transmission may be caused by failure of the en-
gine, the electronic control system, the transmis-
sion proper, or by a combination of these. These
three causes must be distinguished clearly when
performing diagnostics.
15) Diagnostics should be conducted by rotating
with simple, easy operations and proceeding to
complicated, difficult operations. The most impor-
tant thing in diagnostics is to understand the cus-
tomer's complaint, and distinguish between the
three causes.
16) In AT vehicles, do not continue the stall for
more than five seconds at a time (from closed throt-
tle, fully open throttle to stall engine speed).
17) On ABS vehicle, when performing driving test
in jacked-up or lifted-up position, sometimes the
warning light may be lit, but this is not a malfunction
of the system. The reason for this is the speed dif-
ference between the front and rear wheels. After di-
agnosis of engine control system, perform the ABS
memory clearance procedure of self-diagnosis sys-
tem.

B: INSPECTION

Before performing diagnostics, check the following
items which might affect engine problems:

1. BATTERY

1) Measure battery voltage and specific gravity of
electrolyte.

Standard voltage: 12 V

Specific gravity: Above 1.260
2) Check the condition of the main and other fuses,
and harnesses and connectors. Also check for
proper grounding.

2. ENGINE GROUNDING

Make sure the engine grounding terminal is proper-
ly connected to the engine.

EN-00752

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ENGINE (DIAGNOSTICS)

GENERAL DESCRIPTION

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 (MI) 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) and EC instruction No. 98/69/EC. The
OBD system monitors the components and the
system malfunction listed in Engine Section which
affects on emissions.
• When the system decides that a malfunction oc-
curs, MI illuminates. At the same time of the MI illu-
mination 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, MI 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.

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:

• 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.

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).

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ENGINE (DIAGNOSTICS)

GENERAL DESCRIPTION

D: PREPARATION TOOL

ILLUSTRATION

TOOL NUMBER

DESCRIPTION

REMARKS

24082AA210

(Newly adopted 

tool)

CARTRIDGE

Troubleshooting for electrical systems.

22771AA030

SELECT MONI-
TOR KIT

Troubleshooting for electrical systems.
• English: 22771AA030 (Without printer)
• German: 22771AA070 (Without printer)
• French: 22771AA080 (Without printer)
• Spanish: 22771AA090 (Without printer)

ST24082AA210

ST22771AA030