Subaru Legacy III (2000-2003 year). Manual — part 140

EN(H4SO)-172

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

14

CHECK CAUSE OF MISFIRE DIAGNOSED.
Was the cause of misfire diagnosed when the
engine is running?

NOTE:

Disconnected spark plug code, etc.

The cause of misfire found.

Finish diagnostics
operation, if the
engine has no
abnormality.

(1) Repair poor
contact.

NOTE:
In this case, repair
the following:

• Poor contact
in ignitor con-
nector
• Poor contact
in ignition coil
connector
• Poor contact
in fuel injector
connector on
faulty cylinders
• Poor contact
in ECM connec-
tor
• Poor contact
in coupling con-
nector

(2) If there is no
poor contact, con-
tact SUBARU dis-
tributor. Before
contacting, the fol-
lowing items must
be checked:

• Fuel for con-
dition
• Fuel addi-
tives
• Spark plug
for condition
• Plug code for
condition
• Engine oil for
condition

15

CHECK AIR INTAKE SYSTEM.
Is there any fault in air intake system?

There is a fault.

Repair air intake
system.

NOTE:
Check the follow-
ing items:
• Are there air
leaks or air suction
caused by loose or
dislocated nuts
and bolts?
• Are there cracks
or any disconnec-
tion of hoses?

Go to step 16.

Step

Value

Yes

No

EN(H4SO)-173

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

16

CHECK MISFIRE SYMPTOM.
1) Turn ignition switch to ON.
2) Read diagnostic trouble code (DTC).

Does the Subaru Select Monitor or OBD-II
general scan tool indicate only one DTC?

•Subaru Select Monitor
<Ref. to EN(H4SO)-32, Subaru Select Moni-
tor.>
•OBD-II general scan tool
For detailed operation procedures, refer to the
OBD-II General Scan Tool Operation Manual.

NOTE:

Perform diagnosis according to the items listed
below.

Only one DTC indicated.

Go to step 21.

Go to step 17.

17

CHECK DIAGNOSTIC TROUBLE CODE
(DTC) ON DISPLAY.
Does the Subaru Select Monitor or OBD-II
general scan tool indicate DTC P0301 and
P0302?

DTC P0301 and P0302 indi-
cated.

Go to step 22.

Go to step 18.

18

CHECK DIAGNOSTIC TROUBLE CODE
(DTC) ON DISPLAY.
Does the Subaru Select Monitor or OBD-II
general scan tool indicate DTC P0303 and
P0304?

DTC P0303 and P0304 indi-
cated.

Go to step 23.

Go to step 19.

19

CHECK DIAGNOSTIC TROUBLE CODE
(DTC) ON DISPLAY.
Does the Subaru Select Monitor or OBD-II
general scan tool indicate DTC P0301 and
P0303?

DTC P0301 and P0303 indi-
cated.

Go to step 24.

Go to step 20.

20

CHECK DIAGNOSTIC TROUBLE CODE
(DTC) ON DISPLAY.
Does the Subaru Select Monitor or OBD-II
general scan tool indicate DTC P0302 and
P0304?

DTC P0302 and P0304 indi-
cated.

Go to step 25.

Go to step 26.

21

ONLY ONE CYLINDER
Is there any fault in that cylinder?

There is a fault.

Repair or replace
faulty parts.

NOTE:
Check the follow-
ing items.
• Spark plug
• Spark plug cord
• Fuel injector
• Compression
ratio

Go to DTC P0171.
<Ref. to
EN(H4SO)-162,
DTC P0171 —
SYSTEM TOO
LEAN (BANK 1) —
, Diagnostic Pro-
cedure with Diag-
nostic Trouble
Code (DTC).>

Step

Value

Yes

No

EN(H4SO)-174

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

22

GROUP OF #1 AND #2 CYLINDERS
Are there faults in #1 and #2 cylinders?

There are faults.

Repair or replace
faulty parts.

NOTE:
• Check the fol-
lowing items.

• Spark plugs
• Fuel injectors
• Ignition coil
• Compres-
sion ratio

• If no abnormal is
discovered, check
for “IGNITION
CONTROL SYS-
TEM” of #1 and #2
cylinders side.
<Ref. to
EN(H4SO)-72,
IGNITION CON-
TROL SYSTEM,
Diagnostics for
Engine Starting
Failure.>

Go to DTC P0171.
<Ref. to
EN(H4SO)-162,
DTC P0171 —
SYSTEM TOO
LEAN (BANK 1) —
, Diagnostic Pro-
cedure with Diag-
nostic Trouble
Code (DTC).>

23

GROUP OF #3 AND #4 CYLINDERS
Are there faults in #3 and #4 cylinders?

There are faults.

Repair or replace
faulty parts.

NOTE:
• Check the fol-
lowing items.

• Spark plugs
• Fuel injectors
• Ignition coil

• If no abnormal is
discovered, check
for “16. D: IGNI-
TION CONTROL
SYSTEM” of #3
and #4 cylinders
side. <Ref. to
EN(H4SO)-72,
IGNITION CON-
TROL SYSTEM,
Diagnostics for
Engine Starting
Failure.>

Go to DTC P0171.
<Ref. to
EN(H4SO)-162,
DTC P0171 —
SYSTEM TOO
LEAN (BANK 1) —
, Diagnostic Pro-
cedure with Diag-
nostic Trouble
Code (DTC).>

24

GROUP OF #1 AND #3 CYLINDERS
Are there faults in #1 and #3 cylinders?

There are faults.

Repair or replace
faulty parts.

NOTE:
Check the follow-
ing items.
• Spark plugs
• Fuel injectors
• Skipping timing
belt teeth

Go to DTC P0171.
<Ref. to
EN(H4SO)-162,
DTC P0171 —
SYSTEM TOO
LEAN (BANK 1) —
, Diagnostic Pro-
cedure with Diag-
nostic Trouble
Code (DTC).>

Step

Value

Yes

No

EN(H4SO)-175

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

25

GROUP OF #2 AND #4 CYLINDERS
Are there faults in #2 and #4 cylinders?

There are faults.

Repair or replace
faulty parts.

NOTE:
Check the follow-
ing items.
• Spark plugs
• Fuel injectors
• Compression
ratio
• Skipping timing
belt teeth

Go to DTC P0171.
<Ref. to
EN(H4SO)-162,
DTC P0171 —
SYSTEM TOO
LEAN (BANK 1) —
, Diagnostic Pro-
cedure with Diag-
nostic Trouble
Code (DTC).>

26

CYLINDER AT RANDOM
Is the engine idle unstable?

Engine idle is unstable.

Go to DTC P0171.
<Ref. to
EN(H4SO)-162,
DTC P0171 —
SYSTEM TOO
LEAN (BANK 1) —
, Diagnostic Pro-
cedure with Diag-
nostic Trouble
Code (DTC).>

Repair or replace
faulty parts.

NOTE:
Check the follow-
ing items.
• Spark plugs
• Fuel injectors
• Compression
ratio

Step

Value

Yes

No