Subaru Impreza 2003 Service Manual page 554

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
ENGINE (DIAGNOSTICS)
AC: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(H4SO)-46, OP-
ERATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H4SO)-39, OPERATION, Inspec-
tion Mode.>.
Step
1 CHECK EXHAUST SYSTEM.
2 CHECK EGR VALVE.
3 CHECK AIR INTAKE SYSTEM.
4 CHECK PURGE CONTROL SOLENOID
VALVE.
5 CHECK PCV VALVE.
6 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 the 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 the ignition switch to OFF.
2)Connect the connector to fuel pump relay.
3)Disconnect the fuel delivery hose from fuel
filter, and connect fuel pressure gauge.
4)Install the fuel filler cap.
5)Start the engine and idle while gear position
is neutral.
6)Measure the fuel pressure while disconnect-
ing pressure regulator vacuum hose from
intake manifold.
Warning:
Before removing the 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.
Check
Are there holes or loose bolts
on exhaust system?
Is the EGR valve stuck?
Are there holes, loose bolts or
disconnection of hose on air
intake system?
Is the purge control solenoid
valve stuck?
Is PCV valve operated?
Is the fuel pressure 284 — 314
2
kPa (2.9 — 3.2 kg/cm
46 psi)?
EN(H4SO)-142
Yes
Repair exhaust
system.
Replace the EGR
valve.
Repair air intake
system.
Replace the purge
control solenoid
valve.
Go to step 6.
Go to step 7.
, 41 —
No
Go to step 2.
Go to step 3.
Go to step 4.
Go to step 5.
Replace the PCV
valve.
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
supply line