Subaru LEGACY 2003 Service Manual page 84

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
ENGINE (DIAGNOSTICS)
1 CHECK FOR OTHER CAUSES AFFECTING
EXHAUST GAS.
1) Check for use of improper fuel.
2) Check if engine oil or coolant level is
extremely low.
Does CO% after warm-up exceed the spec-
ified value?
2 CHECK EXHAUST SYSTEM.
Is there a fault in exhaust system?
3 CHECK INPUT VOLTAGE FOR OXYGEN
SENSOR.
1) Disconnect connector from oxygen sensor
connector.
2) Measure voltage between main relay and
oxygen sensor.
Connector & terminal
(B18) No. 2 (+) — Chassis ground ( − − − − ):
Does the measured value exceed the spec-
ified value?
4 CHECK HARNESS CONNECTOR BETWEEN
OXYGEN SENSOR AND ENGINE GROUND
TERMINAL.
Measure resistance between oxygen sensor
and chassis ground.
Connector & terminal
(B18) No. 1 — Chassis ground:
Is the measured value less than the specified
value?
5 CHECK OXYGEN SENSOR.
Measure resistance between oxygen sensor
terminals.
Connector & terminal
No. 1 — No. 2:
Is the measured value less than the specified
value?
6 CHECK HARNESS BETWEEN ECM AND OX-
YGEN SENSOR.
1) Disconnect connector from ECM.
2) Measure resistance between ECM and
chassis ground.
Connector & terminal
(B136) No. 7 — Chassis ground:
Does the measured value exceed the spec-
ified value?
Step
EN(H4SOw/oOBD)-82
Value
2%
The system is faulty.
10 V
1Ω
30 Ω
1 MΩ
Yes
Check fuel sys- Go to step 2.
tem.
Repair exhaust Go to step 3.
system.
NOTE:
• Loose installa-
tion of front portion
of exhaust pipe
onto cylinder
heads
• Loose connec-
tion between front
exhaust pipe and
front catalytic con-
verter
• Damage of
exhaust pipe
resulting in hole
Go to step 4. Repair open circuit
between main
relay and oxygen
sensor.
Go to step 5. Repair open circuit
between oxygen
sensor and chas-
sis ground.
Repair poor con- Go to step 6.
tact.
Go to step 7. Repair ground
short circuit
between ECM and
chassis ground.
No