Subaru Forester 2004 Service Manual page 113

Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTIC)
Step
2 CHECK REAR OXYGEN SENSOR DATA.
1) Warm-up the engine until engine coolant
temperature is above 70°C (158°F), and keep
the engine speed at 2,000 rpm to 3,000 rpm for
two minutes.
2) Read the data of rear 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
"READ CURRENT DATA SHOWN ON DIS-
PLAY FOR ENGINE". <Ref. to EN(H4DOTC
2.5)-27, Subaru Select Monitor.>
• OBD-II general scan tool
For detailed operation procedures, refer to the
OBD-II General Scan Tool Operation Manual.
3 CHECK REAR OXYGEN SENSOR DATA.
Read the data of rear oxygen (A/F) sensor sig-
nal using Subaru Select Monitor or OBD-II
general scan tool.
4 CHECK HARNESS BETWEEN ECM AND
REAR OXYGEN SENSOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from ECM and
rear oxygen sensor.
3) Measure the resistance in harness between
ECM and rear oxygen sensor connector.
Connector & terminal
(B137) No. 25 — (T6) No. 4:
5 CHECK HARNESS BETWEEN REAR OXY-
GEN SENSOR AND ECM CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from rear oxygen
sensor.
3) Turn the ignition switch to ON.
4) Measure the voltage between rear oxygen
sensor harness connector and chassis ground.
Connector & terminal
(T6) No. 4 (+) — Chassis ground (
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
Check
Does the value fluctuate?
Is the voltage 0.2 — 0.4 V?
Is the resistance more than 3
Ω?
Is the voltage more than 0.2 V? Replace the rear
−
):
Is there a fault in exhaust sys-
tem?
EN(H4DOTC 2.5)-112
Yes
Go to step 6. Go to step 3.
Go to step 4. Replace the rear
oxygen sensor.
<Ref. to
FU(H4DOTC 2.5)-
38, Rear Oxygen
Sensor.>
Repair open circuit Go to step 5.
in harness between
ECM and rear oxy-
gen sensor connec-
tor.
Repair the har-
oxygen sensor. ness and connec-
<Ref. to tor.
FU(H4DOTC 2.5)-
NOTE:
38, Rear Oxygen
In this case repair
Sensor.>
the following:
• Open circuit in
harness between
rear oxygen sen-
sor and ECM con-
nector
• Poor contact in
rear oxygen sen-
sor connector
• Poor contact in
ECM connector
Repair or replace Replace the rear
the faulty part. oxygen sensor.
<Ref. to
FU(H4DOTC 2.5)-
38, Rear Oxygen
Sensor.>
No