Subaru Legacy III (2000-2003 year). Service manual — part 346

EN(H6DO)-186

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

Step

Value

Yes

No

1

CHECK HARNESS BETWEEN ECM AND
FRONT OXYGEN (A/F) SENSOR CONNEC-
TOR.
1) Turn ignition switch to OFF.
2) Disconnect connectors from ECM and front

oxygen (A/F) sensor connector.

3) Measure resistance of harness between

ECM and front oxygen (A/F) sensor con-
nector.

Connector & terminal

(B137) No. 20 — (E24) No. 4:

Is the measured value less than the speci-
fied value?

1

Ω

Go to step 2.

Repair harness
and connector.

NOTE:
In this case, repair
the following:
• Open circuit in
harness between
ECM and front
oxygen (A/F) sen-
sor connector
• Poor contact in
front oxygen (A/F)
sensor connector
• Poor contact in
ECM connector

2

CHECK HARNESS BETWEEN ECM AND
FRONT OXYGEN (A/F) SENSOR CONNEC-
TOR.
Measure resistance of harness between ECM
and front oxygen (A/F) sensor connector.

Connector & terminal

(B137) No. 30 — (E24) No. 3:

Is the measured value less than the specified
value?

1

Ω

Go to step 3.

Repair harness
and connector.

NOTE:
In this case, repair
the following:
• Open circuit in
harness between
ECM and front
oxygen (A/F) sen-
sor connector
• Poor contact in
front oxygen (A/F)
sensor connector
• Poor contact in
ECM connector

3

CHECK POOR CONTACT.
Check poor contact in front oxygen (A/F) sen-
sor connector.
Is there poor contact in front oxygen (A/F) sen-
sor connector?

There is poor contact.

Repair poor con-
tact in front oxygen
(A/F) sensor con-
nector.

Replace front oxy-
gen (A/F) sensor.
<Ref. to
FU(H6DO)-43,
Front Oxygen (A/
F) Sensor.>

EN(H6DO)-187

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

AE:DTC P0171 — SYSTEM TOO LEAN (BANK 1) —

NOTE:
For the diagnostic procedure, refer to DTC P0172. <Ref. to EN(H6DO)-188, DTC P0172 — SYSTEM TOO
RICH (BANK 1) —, Diagnostic Procedure with Diagnostic Trouble Code (DTC).>

EN(H6DO)-188

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

AF:DTC P0172 — SYSTEM TOO RICH (BANK 1) —

• DTC DETECTING CONDITION:

• Two consecutive driving cycles with fault

• TROUBLE SYMPTOM:

• Erroneous idling
• Engine stalls.
• Poor driving performance

CAUTION:
After repair or replacement of faulty parts, conduct Clear Memory Mode <Ref. to EN(H6DO)-54, OP-
ERATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H6DO)-47, OPERATION, Inspec-
tion Mode.>.

Step

Value

Yes

No

1

CHECK ANY OTHER DTC ON DISPLAY.
Is any other DTC displayed?

Another DTC is displayed.

Inspect the rele-
vant DTC using
“List of Diagnostic
Trouble Code
(DTC)”. <Ref. to
EN(H6DO)-89, List
of Diagnostic
Trouble Code
(DTC).>

Go to step 2.

2

CHECK EXHAUST SYSTEM.
Are there holes or loose bolts on exhaust sys-
tem?

Holes or loose bolts are found. Repair exhaust

system.

Go to step 3.

3

CHECK AIR INTAKE SYSTEM.
Are there holes, loose bolts or disconnection of
hose on air intake system?

Holes, loose bolts or discon-
nection of hose is found.

Repair air intake
system.

Go to step 4.

4

CHECK FUEL PRESSURE.

Warning:

• Place “NO FIRE” signs near the working
area.
• Be careful not to spill fuel on the floor.

1) Lower fuel pressure.

(1) Disconnect connector from fuel pump

relay.

(2) Start the engine and run it until it stalls.
(3) After the engine stalls, crank it for five

more seconds.

(4) Turn ignition switch to OFF.

2) Connect connector to fuel pump relay.
3) Disconnect fuel delivery hose from fuel fil-

ter, and connect fuel pressure gauge.

4) Install fuel filler cap.
5) Start the engine and idle while gear position

is neutral.

6) Measure fuel pressure while disconnecting

pressure regulator vacuum hose from
intake manifold.
Is the measured value within the specified
range?

Warning:

Before removing fuel pressure gauge, lower
fuel pressure.

NOTE:

If fuel pressure does not increase, squeeze fuel
return hose 2 to 3 times, then measure fuel
pressure again.

284 — 314 kPa (2.9 — 3.2 kg/

cm

2

, 41 — 46 psi)

Go to step 5.

Repair the follow-
ing items.
Fuel pressure too
high
• Clogged fuel
return line or bent
hose
Fuel pressure too
low
• Improper fuel
pump discharge
• Clogged fuel sup-
ply line

EN(H6DO)-189

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

5

CHECK FUEL PRESSURE.
After connecting pressure regulator vacuum
hose, measure fuel pressure.
Is the measured value within the specified
range?

Warning:

Before removing fuel pressure gauge, lower
fuel pressure.

NOTE:

• If fuel pressure does not increase, squeeze
fuel return hose 2 to 3 times, then measure
fuel pressure again.
• If out of specification as measured at this
step, check or replace pressure regulator and
pressure regulator vacuum hose.

206 — 235 kPa (2.1 — 2.4 kg/

cm

2

, 30 — 34 psi)

Go to step 6.

Repair the follow-
ing items.
Fuel pressure too
high
• Faulty pressure
regulator
• Clogged fuel
return line or bent
hose
Fuel pressure too
low
• Faulty pressure
regulator
• Improper fuel
pump discharge
• Clogged fuel sup-
ply line

6

CHECK FUEL INJECTOR.
1) Turn ignition switch to OFF.
2) Remove right bank fuel injector. <Ref. to

FU(H6DO)-39, REMOVAL, Fuel Injector.>

3) Check fuel injector

Is fuel injector clogged?

Fuel injector is clogged.

Replace fuel injec-
tor. <Ref. to
FU(H6DO)-39,
Fuel Injector.>

Go to step 7.

7

CHECK FUEL INJECTOR.
Measure resistance between terminals of fuel
injector.

Terminals

No. 1 — No. 2

Is the measured value within the specified
range?

5 — 20

Ω

Go to step 8.

Replace fuel injec-
tor. <Ref. to
FU(H6DO)-39,
Fuel Injector.>

8

CHECK ENGINE COOLANT TEMPERATURE
SENSOR.
1) Start the engine and warm-up completely.
2) Read data of engine coolant temperature

sensor signal using Subaru Select Monitor
or OBD-II general scan tool.
Does the measured value exceed the spec-
ified value?

NOTE:

• Subaru Select Monitor
For detailed operation procedure, refer to the
“READ CURRENT DATA FOR ENGINE”.
<Ref. to EN(H6DO)-34, Subaru Select Moni-
tor.>
• OBD-II general scan tool
For detailed operation procedures, refer to the
OBD-II General Scan Tool Instruction Manual.

75

°

C (167

°

F)

Go to step 9.

Replace engine
coolant tempera-
ture sensor. <Ref.
to FU(H6DO)-29,
Engine Coolant
Temperature Sen-
sor.>

Step

Value

Yes

No