Subaru Forester 2004 Service Manual page 77

Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTIC)
Step
1 CHECK GROUND CIRCUIT FOR ECM.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from ECM.
3) Measure the resistance of harness
between ECM connector and chassis ground.
Connector & terminal
(B134) No. 6 — Chassis ground:
(B134) No. 7 — Chassis ground:
2 CHECK CURRENT DATA.
1) Start the engine.
2) Read the data of rear 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.
3 CHECK OUTPUT SIGNAL FROM ECM.
1) Start and idle the engine.
2) Measure the voltage between ECM con-
nector and chassis ground.
Connector & terminal
(B135) No. 2 (+) — Chassis ground (
4 CHECK OUTPUT SIGNAL FROM ECM.
Measure the voltage between ECM connector
and chassis ground.
Connector & terminal
(B135) No. 2 (+) — Chassis ground (
5 CHECK OUTPUT SIGNAL FROM ECM.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from rear oxygen
sensor.
3) Measure the voltage between ECM con-
nector and chassis ground.
Connector & terminal
(B135) No. 2 (+) — Chassis ground (
Check
Is the resistance less than 5
Ω?
Is the current more than 0.2 A? Repair the connec-
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?
Is the voltage less than 1 V?
−
):
EN(H4DOTC 2.5)-76
Yes
Go to step 2. Repair the har-
ness and connec-
tor.
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 3.
tor.
NOTE:
In this case repair
the following:
• Poor contact in
rear oxygen sen-
sor connector
• Poor contact in
rear oxygen sen-
sor connecting
harness connector
• Poor contact in
ECM connector.
Go to step 6. Go to step 4.
Repair the poor Go to step 5.
contact in ECM
connector.
Replace the ECM. Repair battery short
<Ref. to circuit in harness
FU(H4DOTC 2.5)- between ECM and
41, Engine Con- rear oxygen sensor
trol Module connector. After
(ECM).> repair, replace the
ECM. <Ref. to
FU(H4DOTC 2.5)-
41, Engine Con-
trol Module
(ECM).>
No