Subaru 2002 IMPREZA Service Manual page 673

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
Step
2 CHECK FRONT OXYGEN (A/F) 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 (160°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-34, Subaru Select Monitor.>
•OBD-II general scan tool
For detailed operation procedures, refer to the
OBD-II General Scan Tool Instruction Manual.
3 CHECK FRONT OXYGEN (A/F) SENSOR DA-
TA.
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 the accelerator pedal, taking
approx. 5 seconds, and quickly release the ac-
celerator pedal to decrease engine speed.
4 CHECK HARNESS BETWEEN ECM AND
FRONT OXYGEN (A/F) SENSOR.
1)Turn the ignition switch to OFF.
2)Disconnect the connector from ECM and
front oxygen (A/F) sensor connector.
3)Measure the resistance between ECM and
front oxygen (A/F) sensor.
Connector & terminals
(B136) No. 6 — (E24) No. 3:
(B136) No. 7 — (E24) No. 4:
(B136) No. 19 — (E24) No. 1:
(B136) No. 20 — (E24) No. 6:
5 CHECK HARNESS BETWEEN ECM AND
FRONT OXYGEN (A/F) SENSOR.
Measure the resistance between ECM and
chassis ground.
Connector & terminals
(B136) No. 6 — Chassis ground:
(B136) No. 7 — Chassis ground:
(B136) No. 19 — Chassis ground:
(B136) No. 20 — Chassis ground:
6 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 the value equal to or more
than 0.85 and equal to less
than 1.15 in idling?
Is the value more than 1.1 for a
moment?
Is the resistance less than 5
Ω?
Is the resistance more than 1
MΩ?
Is there a fault in exhaust sys-
tem?
EN-241
ENGINE (DIAGNOSTICS)
Yes
Go to step 3. Go to step 4.
Go to step 6. Go to step 4.
Go to step 5. Repair the open
circuit between
ECM and front
oxygen (A/F) sen-
sor.
Go to step 6. Repair the ground
short circuit
between ECM and
front oxygen (A/F)
sensor.
Repair or replace Replace the front
the faulty parts. oxygen (A/F) sen-
sor. <Ref. to FU-
47, Front Oxygen
(A/F) Sensor.>
No