Subaru Legacy (2005 year). Manual - part 423

EN(H6DO)(diag)-5

ENGINE (DIAGNOSTICS)

General Description

3. General Description

A: CAUTION

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

CAUTION:
• All airbag system wiring harnesses and con-
nectors are yellow. Do not use the electrical
test equipment on these circuits.
• Be careful not to damage the airbag system
wiring harness when servicing the ECM, 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 parts will be dam-
aged.
3) Do not disconnect the battery terminals while the
engine is running.
A large counter electromotive force will be generat-
ed in the generator, and this voltage may damage
electronic parts such as ECM.
4) Before disconnecting the connectors of each
sensor and ECM, be sure to turn the ignition switch
to OFF. Perform the clear memory mode after con-
necting the connectors.
5) Poor contact has been identified as a primary
cause of this problem. Measure the voltage or re-
sistance of each sensor or all electrical control
modules using 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 parts.
6) Remove the ECM from the located position after
disconnecting two cables on battery.
Otherwise, the ECM may be damaged.

CAUTION:
When replacing the ECM, be careful not to use 
the ECM with wrong specifications to avoid any 
damage on the fuel injection system.
7) Connectors of each sensor in the engine com-
partment and the harness connectors on the en-
gine 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 as the grounding
point to chassis when measuring voltage and resis-
tance in the passenger compartment.

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

10) Every MFI-related part is a precision part. Do
not drop them.
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 module.
• 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 mentioned
above.
• 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 until it stops.

(A) Stud bolt

EN-00001

(A)

EN-02473

EN(H6DO)(diag)-6

ENGINE (DIAGNOSTICS)

General Description

13) Diagnostics should be conducted by starting
with simple, easy operations then proceeding to
complicate, difficult operations. The most important
thing in diagnostics is to understand the customer’s
complaint, and distinguish the cause among en-
gine, electrical system and transmission.
14) For the model with ABS, the ABS warning light
may illuminates when performing driving test with
jacked-up or lifted-up condition, but this is not a
system malfunction. This is due to speed difference
between the front and rear wheels. After diagnosis
of engine control system, perform the ABS memory
clear procedure of self-diagnosis function.

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 main and other fuses,
and harnesses and connectors. Also check for
proper grounding.

2. ENGINE GROUND

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

C: NOTE

1. GENERAL DESCRIPTION

• On-board diagnostic (OBD) system detects and
indicates a fault in various inputs and outputs of the
complex electronic control. Malfunction indicator
light 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 E-OBD reg-
ulation. The OBD system monitors the components

and the system malfunction listed in Engine Sec-
tion which affects on emissions.
• When the system decides that a malfunction oc-
curs, malfunction indicator light illuminates. At the
same time of the malfunction indicator light illumi-
nation or blinking, the DTC and a freeze frame en-
gine 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, malfunction indi-
cator light is turned off, but DTC remains at on-
board computer.
• When troubleshooting the vehicles complied with
E-OBD regulation, connect Subaru Select Monitor
or the general scan tool to the vehicle.

2. ENGINE AND EMISSION CONTROL SYS-
TEM

• MFI system is a system that supplies the opti-
mum air-fuel mixture to the engine for all the vari-
ous operating conditions through the use of the
latest electronic technology. 
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 sig-
nal 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.
• Excellent engine start and warm-up perfor-
mance by the correction of engine coolant tem-
perature and intake air temperature.

EN-02473

EN(H6DO)(diag)-7

ENGINE (DIAGNOSTICS)

General Description

D: PREPARATION TOOL

ILLUSTRATION

TOOL NUMBER

DESCRIPTION

REMARKS

18482AA000

(Newly adopted tool)

CARTRIDGE

Troubleshooting for electrical system.

22771AA030

SUBARU SELECT 
MONITOR KIT

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

ST18482AA000

ST22771AA030

EN(H6DO)(diag)-8

ENGINE (DIAGNOSTICS)

Electrical Component Location

4. Electrical Component Location

A: LOCATION

1. CONTROL MODULE

• LHD model

• RHD model

(1)

Engine control module (ECM)

(3)

Test mode connector

(4)

Data link connector

(2)

Malfunction indicator light

(1)

(4)

(3)

(2)

EN-02474

(1)

(4)

(2)

(3)

EN-02475