Subaru LEGACY 2004 Service Manual page 753

Diagnostic Procedure with Diagnostic Trouble Code (DTC)
Y: 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 2.5)(diag)-
41, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H4SO 2.5)(diag)-34, Inspection Mode.>.
Step
1 CHECK OPTION CODE.
2 CHECK EXHAUST SYSTEM.
3 CHECK AIR INTAKE SYSTEM.
4 CHECK EGR VALVE.
5 CHECK PURGE CONTROL SOLENOID
VALVE.
6 CHECK PCV VALVE.
Check
Is the option code EC, EK or
K4?
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?
EN(H4SO 2.5)(diag)-137
ENGINE (DIAGNOSTICS)
Yes
Go to step 2. Refer to EN(H4SO
2.0) section. <Ref.
to EN(H4SO
2.0)(diag)-66, List
of Diagnostic Trou-
ble Code (DTC).>
NOTE:
Fuel injection sys-
tem for KA and KS
model is the same
as 2.0 L model.
Repair exhaust Go to step 3.
system.
Repair air intake Go to step 4.
system.
Replace the EGR Go to step 5.
valve.
Replace the purge Go to step 6.
control solenoid
valve.
Replace the PCV Go to step 7.
valve.
No