Subaru Impreza 2003 Service Manual page 551

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
Step
5 CHECK EXHAUST SYSTEM.
Check exhaust system parts.
NOTE:
Check the following items.
•Loose installation of portions
•Damage (crack, hole etc.) of parts
•Looseness and ill fitting of parts between front
oxygen (A/F) sensor and rear oxygen sensor
Check
Is there a fault in exhaust sys-
tem?
EN(H4SO)-139
ENGINE (DIAGNOSTICS)
Yes
Repair or replace Replace the rear
faulty parts. oxygen sensor.
<Ref. to
FU(H4SO)-44,
Front Oxygen (A/
F) Sensor.>
No