Subaru Impreza 2004 Service Manual page 66

Diagnostic Procedure with Diagnostic Trouble Code (DTC)
Step
4 CHECK FUEL PRESSURE.
After connecting the pressure regulator vac-
uum hose, measure fuel pressure.
Warning:
Before removing the fuel pressure gauge,
release fuel pressure.
NOTE:
•If the 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 the pressure regulator and
pressure regulator vacuum hose.
5 CHECK ENGINE COOLANT TEMPERATURE
SENSOR.
1)Start the engine and warm-up completely.
2)Read the 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(H4DOTC)(diag)-32, Subaru
Select Monitor.>
•OBD-II general scan tool
For detailed operation procedures, refer to the
OBD-II General Scan Tool Instruction Manual.
6 CHECK MASS AIR FLOW AND INTAKE AIR
TEMPERATURE.
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 the A/C switch to OFF.
4)Turn all accessory switches to OFF.
5)Read the data of mass air flow and intake air
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(H4DOTC)(diag)-32, Subaru
Select Monitor.>
•OBD-II general scan tool
For detailed operation procedure, refer to the
OBD-II General Scan Tool Instruction Manual.
Check
Is the measured value 206 —
235 kPa (2.1 — 2.4 kg/cm
— 34 psi)?
Is the temperature more than
60°C (140°F)?
Is the measured value within
the followings? 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)
EN(H4DOTC)(diag)-145
ENGINE (DIAGNOSTICS)
Yes
Go to step 5. Repair the follow-
2 ing items.
, 30
Fuel pressure too
high:
Fuel pressure too
low:
Go to step 6. Replace the
engine coolant
temperature sen-
sor. <Ref. to
FU(H4DOTC)-28,
Engine Coolant
Temperature Sen-
sor.>
Go to step 7. Replace the mass
air flow and intake
air temperature
sensor. <Ref. to
FU(H4DOTC)-34,
Mass Air Flow and
Intake Air Temper-
ature Sensor.>
No
• Faulty pres-
sure regulator
• Clogged fuel
return line or
bent hose
• Faulty pres-
sure regulator
• Improper fuel
pump discharge
• Clogged fuel
supply line