Subaru FORESTER 2001 Service Manual page 92

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
No.
1 CHECK ANY OTHER DTC ON DISPLAY.
2 CHECK POWER SUPPLY TO FRONT OXY-
GEN (A/F) SENSOR.
1) Turn ignition switch to OFF.
2) Disconnect connector from front oxygen
(A/F) sensor.
3) Turn ignition switch to ON.
4) Measure voltage between front oxygen
(A/F) sensor connector and engine ground.
Connector & terminal
(B18) No. 2 (+) — Engine ground (−):
3 CHECK GROUND CIRCUIT OF ECM.
Measure resistance of harness between ECM
connector and chassis ground.
Connector & terminal
(B137) No. 8 — Chassis ground:
(B137) No. 9 — Chassis ground:
4 CHECK CURRENT DATA.
1) Start engine
2) Read data of front oxygen (A/F) sensor
heater current using Subaru Select Monitor or
OBD-II general scan tool.
NOTE:
¼ Subaru Select Monitor
For detailed operation procedure, refer to the
"READ CURRENT DATA FOR ENGINE".
<Ref. to EN(DOHC TURBO)-36, Subaru
Select Monitor.>
¼ OBD-II scan tool
For detailed operation procedures, refer to the
OBD-II General Scan Tool Instruction Manual.
5 CHECK OUTPUT SIGNAL FROM ECM.
1) Start and idle the engine.
2) Measure voltage between ECM connector
and chassis ground.
Connector & terminal
(B137) No. 4 (+) — Chassis ground (−):
(B137) No. 5 (+) — Chassis ground (−):
Step
Does the Subaru Select
Monitor or OBD-II general
scan tool indicate DTC
P0031 and P0037 at the
same time?
Is the voltage more than 10
V?
Is the resistance less than
5 Ω?
Is the value more than 0.2
A?
Is the voltage less than 1.0
V?
EN(DOHC TURBO)-91
Check Yes
Go to step 2.
Go to step 3.
Go to step 4.
Repair poor con-
tact in connector.
NOTE:
In this case,
repair the follow-
ing:
¼ Poor contact in
front oxygen (A/F)
sensor connector
¼ Poor contact in
ECM connector
Go to step 7.
Engine (Diagnostics)
No
Go to step 5.
Repair power sup-
ply line.
NOTE:
In this case,
repair the follow-
ing:
¼ Open circuit in
harness between
main relay and
front oxygen (A/F)
sensor connector
¼ Poor contact in
front oxygen (A/F)
sensor connector
¼ Poor contact in
main relay con-
nector
Repair harness
and connector.
NOTE:
In this case,
repair the follow-
ing:
¼ Open circuit in
harness between
ECM and engine
ground terminal
¼ Poor contact in
ECM connector
Poor contact in
coupling connec-
tor
Go to step 5.
Go to step 6.