DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
Z: DTC P0172 — FUEL TRIM MALFUNCTION (A/F TOO RICH) —
• 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

Step Check Yes No
1 CHECK EXHAUST SYSTEM. Are there holes or loose bolts
on exhaust system?

Repair exhaust
system.


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

Repair air intake
system.


3 CHECK FUEL PRESSURE

Warning:
•Place “NO FIRE” signs near the working
area.
•Be careful not to spill fuel on the floor.
1)Release 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 filter,
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.
Warning:
Before removing fuel pressure gauge, release
fuel pressure.
NOTE:
If fuel pressure does not increase, squeeze fuel
return hose 2 to 3 times, then measure fuel
pressure again.
Is fuel pressure between 284
and 314 kPa (2.9 — 3.2 kg/
cm2, 41 — 46 psi)?
Go to step 4. Repair the following
items.
Fuel pressure too
high
• Clogged fuel
return line or bent
hose
Fuel pressure too
low
• Improper fuel
pump discharge
• Clogged fuel
supply line
EN(DOHC TURBO)-146
ENGINE (DIAGNOSTICS)
DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)


4 CHECK FUEL PRESSURE.
After connecting pressure regulator vacuum
hose, measure fuel pressure.
Warning:
Before removing fuel pressure gauge, release
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.
Is fuel pressure between 206
and 235 kPa (2.1 — 2.4 kg/
cm2, 30 — 34 psi)?
Go to step 5. Repair the following
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
supply line


5 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.
NOTE:
•Subaru Select Monitor
For detailed operation procedure, refer to the
“READ CURRENT DATA FOR ENGINE”.
<Ref. to EN(DOHC TURBO)-28, Subaru
Select Monitor.>
•OBD-II general scan tool
For detailed operation procedures, refer to the
OBD-II General Scan Tool Instruction Manual.
Is temperature greater than
60°C (140°F)?
Go to step 6. Replace engine
coolant temperature
sensor. <Ref.
to FU(DOHC
TURBO)-27,
Engine Coolant
Temperature Sensor.>


6 CHECK INTAKE MANIFOLD PRESSURE
SENSOR.
1)Start the engine and warm-up engine until
coolant temperature is greater than 60°C
(140°F).
2)Place the shift lever in neutral position.
3)Turn A/C switch to OFF.
4)Turn all accessory switches to OFF.
5)Read data of intake manifold pressure sensor
signal using Subaru Select Monitor or
OBD-II general scan tool.
NOTE:
•Subaru Select Monitor
For detailed operation procedure, refer to the
“READ CURRENT DATA FOR ENGINE”.
<Ref. to EN(DOHC TURBO)-28, Subaru
Select Monitor.>
•OBD-II general scan tool
For detailed operation procedure, refer to the
OBD-II General Scan Tool Instruction Manual.
Specification:
•Intake manifold absolute pressure
Ignition ON
73.3 — 106.6 kPa (550 — 800 mmHg,
21.65 — 31.50 inHg)
Idling
24.0 — 41.3 kPa (180 — 310 mmHg, 7.09
— 12.20 inHg)
Is the value within the specifications?
Go to step 7. Replace mass air
flow and intake
manifold pressure
sensor. <Ref. to
FU(DOHC
TURBO)-32, Mass
Air Flow and
Intake Air Temperature
Sensor.>