Subaru Legacy 2004 Service Manual page 558

Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTICS)
W: DTC P0171 SYSTEM TOO LEAN (BANK 1)
Refer to DTC P0172 for diagnostic procedure. <Ref. to EN(H4SO 2.0)(diag)-126, DTC P0172 SYSTEM TOO
RICH (BANK 1), Diagnostic Procedure with Diagnostic Trouble Code (DTC).>
X: 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 2.0)(diag)-
38, OPERATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H4SO 2.0)(diag)-32, OPER-
ATION, Inspection Mode.>.
Step
1 CHECK EXHAUST SYSTEM.
2 CHECK AIR INTAKE SYSTEM.
3 CHECK EGR VALVE.
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.
1) Release the 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, and con-
nect the fuel pressure gauge.
4) Install the fuel filler cap.
5) Start the engine and idle while gear posi-
tion is neutral.
6) Measure the fuel pressure while discon-
necting pressure regulator vacuum hose from
intake manifold.
Warning:
Release fuel pressure before removing the
fuel pressure gauge,.
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?
Are there holes, loose bolts or
disconnection of hose on air
intake system?
Is the EGR valve stuck?
Is the purge control solenoid
valve stuck?
Is the PCV valve stuck?
Is fuel pressure 284 — 314
kPa (2.9 — 3.2 kg/cm
46 psi)?
EN(H4SO 2.0)(diag)-126
Yes
Repair the exhaust
system.
Repair the air
intake system.
Replace the EGR
valve.
Replace the purge
control solenoid
valve.
Replace the PCV
valve.
Go to step 7.
2
, 41 —
No
Go to step 2.
Go to step 3.
Go to step 4.
Go to step 5.
Go to step 6.
Repair the follow-
ing items.
Fuel pressure is
too high:
• Clogged fuel
return line or
bent hose
Fuel pressure is
too low:
• Improper fuel
pump discharge
• Clogged fuel
supply line