Subaru LEGACY 2003 Service Manual page 96

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
ENGINE (DIAGNOSTICS)
1 CHECK INPUT SIGNAL FOR ECM.
1) Turn ignition switch to ON.
2) Measure voltage between ECM and chas-
sis ground.
Connector & terminal
(B136) No. 12 (+) — Chassis ground (–):
Is the measured value within the specified
value?
2 CHECK POOR CONTACT.
Is there poor contact in ECM connector?
3 CHECK HARNESS BETWEEN CO RESIS-
TOR AND ECM CONNECTOR.
1) Turn ignition switch to OFF.
2) Disconnect connector from ECM and CO
resistor.
3) Measure resistance of harness between
ECM and CO resistor connector.
Connector & terminal
(B136) No. 15 — (B155) No. 1:
(B136) No. 12 — (B155) No. 2:
(B136) No. 16 — (B155) No. 3:
Is the measured value less than the speci-
fied value?
4 CHECK HARNESS BETWEEN CO RESIS-
TOR AND ECM CONNECTOR.
Measure resistance of harness between ECM
connector and chassis ground.
Connector & terminal
(B136) No. 15 — Chassis ground:
(B136) No. 12 — Chassis ground:
(B136) No. 16 — Chassis ground:
Does the measured value exceed the specified
value?
5 CHECK CO RESISTOR.
Measure resistance between CO resistor ter-
minals.
Terminals
No. 1 — No. 3:
Is the measured value within the specified
value?
6 CHECK CO RESISTOR.
Measure variable resistance between CO
resistor terminals while rotating the screw of
CO resistor.
Terminals
No. 1 — No. 2:
Is the measured value within the specified
value?
Step
EN(H4SOw/oOBD)-94
Value
0.5 — 4.5 V
There is poor contact.
1 Ω
1 MΩ
4 — 6 kΩ
0 — 6 kΩ
Yes
Go to step 3. Go to step 2.
Repair poor con- Replace ECM.
tact in ECM con- <Ref. to
nector. FU(H4SOw/
oOBD)-42, Engine
Control Module.>
Go to step 4. Repair open circuit
in harness
between ECM and
CO resistor con-
nector.
Go to step 5. Repair short circuit
in harness
between ECM and
CO resistor con-
nector.
Go to step 6. Replace CO resis-
tor.
Replace ECM. Replace CO resis-
tor.
NOTE:
Ensure resistance
varies in response
to screw rotation.
No