Subaru Impreza 2003 Service Manual page 1312

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
ENGINE (DIAGNOSTICS)
Step
1 CHECK ANY OTHER DTC ON DISPLAY.
2 CHECK FRONT (A/F) OXYGEN SENSOR DA-
TA.
1)Start the engine.
2)While observing the Subaru Select Monitor
or OBD-II general scan tool screen, warm-up
the engine until coolant temperature is above
70°C (158°F).
If the engine is already warmed-up, operate at
idle speed for at least 1 minute.
3)Read the data of front oxygen (A/F) sensor
signal using Subaru Select Monitor or OBD-II
general scan tool.
NOTE:
•Subaru Select Monitor
For detailed operation procedure, refer to the
"READ CURRENT DATA FOR ENGINE".
<Ref. to EN(H4DOTC)-32, Subaru Select Mon-
itor.>
•OBD-II general scan tool
For detailed operation procedures, refer to the
OBD-II General Scan Tool Instruction Manual.
3 CHECK REAR OXYGEN SENSOR SIGNAL.
1)Race the engine at speeds from idling to
5,000 rpm for a total of 5 cycles.
NOTE:
To increase the engine speed to 5,000 rpm,
slowly depress accelerator pedal, taking ap-
prox. 5 seconds, and quickly release accelera-
tor pedal to decrease engine speed.
2)Operate the LED operation mode for engine.
NOTE:
•Subaru Select Monitor
For detailed operation procedure, refer to the
"LED OPERATION MODE FOR ENGINE".
<Ref. to EN(H4DOTC)-32, Subaru Select Mon-
itor.>
4 CHECK EXHAUST SYSTEM.
Check the exhaust system parts.
NOTE:
Check the following items.
•Loose installation of portions
•Damage (crack, hole etc.) of parts
•Looseness of front oxygen (A/F) sensor
•Looseness and ill fitting of parts between front
oxygen (A/F) sensor and rear oxygen sensor
Check
Is any other DTC displayed?
Is the measured value 0.85 —
1.15 (in idling)?
Does the LED of {Rear O
Signal} blink?
Is there a fault in exhaust sys-
tem?
EN(H4DOTC)-136
Yes
Inspect the rele-
vant DTC using
"List of Diagnostic
Trouble Code
(DTC)". <Ref. to
EN(H4DOTC)-75,
List of Diagnostic
Trouble Code
(DTC).>
Go to step 3.
Rich Repair the poor
2
contact in front
oxygen (A/F) sen-
sor and rear oxy-
gen sensor
connector.
Repair or replace
the faulty parts.
No
Go to step 2.
Go to step 4.
Check the rear
oxygen sensor cir-
cuit. <Ref. to
FU(H4DOTC)-46,
Rear Oxygen Sen-
sor.>
Replace the front
oxygen (A/F) sen-
sor. <Ref. to
FU(H4DOTC)-44,
Front Oxygen (A/
F) Sensor.>