Subaru Legacy 2004 Service Manual page 1392

Diagnostic Procedure with Diagnostic Trouble Code (DTC)
Step
6 CHECK EXHAUST SYSTEM.
Check exhaust system parts.
NOTE:
Check the following items:
• Loose part of exhaust system and incom-
plete installation
• Damage (crack, hole etc.) of parts
• Looseness and ill fitting of parts between
front oxygen (A/F) sensor and rear oxygen
sensor
T: DTC P0171 SYSTEM TOO LEAN (BANK 1)
NOTE:
For diagnostic procedure, refer to DTC P0172. <Ref. to EN(H4DOTC)(diag)-104, DTC P0172 SYSTEM TOO
RICH (BANK 1), Diagnostic Procedure with Diagnostic Trouble Code (DTC).>
Check
Is there a fault in exhaust sys-
tem?
EN(H4DOTC)(diag)-103
ENGINE (DIAGNOSTICS)
Yes
Repair or replace Replace the rear
the faulty part. oxygen sensor.
<Ref. to
FU(H4DOTC)-34,
Rear Oxygen Sen-
sor.>
No