Subaru Forester 2004 Service Manual page 72

Diagnostic Procedure with Diagnostic Trouble Code (DTC)
Step
1 CHECK POWER SUPPLY TO FRONT OXY-
GEN (A/F) SENSOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from front oxygen
(A/F) sensor.
3) Turn the ignition switch to ON.
4) Measure the voltage between front oxygen
(A/F) sensor connector and engine ground.
Connector & terminal
(B262) No. 1 (+) — Engine ground (
2 CHECK GROUND CIRCUIT FOR ECM.
Measure the resistance of harness between
ECM connector and chassis ground.
Connector & terminal
(B134) No. 6 — Chassis ground:
(B134) No. 7 — Chassis ground:
3 CHECK CURRENT DATA.
1) Start the engine.
2) Read the data of front oxygen (A/F) sensor
heater current 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.
4 CHECK OUTPUT SIGNAL FROM ECM.
1) Start and idle the engine.
2) Measure the voltage between ECM con-
nector and chassis ground.
Connector & terminal
(B134) No. 2 (+) — Chassis ground (
(B134) No. 3 (+) — Chassis ground (
5 CHECK OUTPUT SIGNAL FROM ECM.
Measure the voltage between ECM connector
and chassis ground.
Connector & terminal
(B134) No. 2 (+) — Chassis ground (
(B134) No. 3 (+) — Chassis ground (
Check
Is the voltage more than 10 V? Go to step 2.
−
):
Is the resistance less than 5
Ω?
Is the current more than 0.2 A? Repair poor con-
Is the voltage less than 1 V?
−
):
−
):
Does the voltage change by
shaking the harness and con-
nector of ECM while monitor-
ing the value with voltage
−
): meter?
−
):
EN(H4DOTC 2.5)-71
ENGINE (DIAGNOSTIC)
Yes
Repair the power
supply line.
NOTE:
In this case repair
the following:
• Open circuit in
harness between
main relay and
front oxygen (A/F)
sensor connector
• Poor contact in
front oxygen (A/F)
sensor connector
• Poor contact in
main relay connec-
tor
Go to step 3. Repair the harness
and connector.
NOTE:
In this case repair
the following:
• Open circuit in
harness between
ECM and engine
ground cable
• Poor contact in
ECM connector.
• Poor contact in
coupling connector
Go to step 4.
tact connector.
NOTE:
In this case repair
the following:
• Poor contact in
front oxygen (A/F)
sensor connector
• Poor contact in
ECM connector.
Go to step 6. Go to step 5.
Repair the poor Go to step 6.
contact in ECM
connector.
No