Subaru Legacy III (2000-2003 year). Manual - part 459

EN(H4DOSTC)-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 the Airbag system
wiring harness when servicing the engine con-
trol module (ECM), transmission control mod-
ule (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 cables 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 ECM, be sure to turn OFF the ignition
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 the 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 or TCM mounting stud bolts at the
body head grounding point when measuring the
voltage and resistance inside the passenger com-
partment.

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

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

(A) Stud bolt

EN-00001

( A )

EN-00154

( A )

EN-00952

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ENGINE (DIAGNOSTICS)

GENERAL DESCRIPTION

11) 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 ECM.
12) 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.
13) 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.
14) 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.
15) On ABS vehicle, when performing a 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 the 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.

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.

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 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.

EN-00952

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ENGINE (DIAGNOSTICS)

GENERAL DESCRIPTION

• 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).

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

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ENGINE (DIAGNOSTICS)

ELECTRICAL COMPONENTS LOCATION

4. Electrical Components Location

A: LOCATION

1. ENGINE

• MODULE

(1) Engine control module (ECM)

(3) Read memory connector

(2) CHECK ENGINE malfunction indi-

cator lamp (MI)

(4) Test mode connector

(5) Data link connector

EN-00953

(4)

(2)

(1)

(3)

(5)

EN-00954

( 1 )

(2)

EN-00956

EN-00955

(4)

(3)

EN-00957

(5)