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