sensor SUBARU LEGACY 1995 Service Repair Manual

OBD0191
I: DTC P0125
—INSUFFICIENT COOLANT TEMPERATURE
FOR CLOSED LOOP FUEL CONTROL
(TW
—CL)—
DESCRIPTION:
Refer to“F: DTC P0115—ENGINE COOLANT TEM-
PERATURE SENSOR CIRCUIT MALFUNCTION—
[T11F0]”.
DTC DETECTING CONDITION:

Two consecutive trips with fault
TROUBLE SYMPTOM:

Engine would not return to idling.
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11. Diagnostics Chart with Trouble Code

1.Check DTC P0115 on display.
No
Ye s

Inspect DTC P0115 using“11. Diagnostics Chart
with Trouble Code [T1100]”.

In this case, it is unnecessary to inspect DTC
P0125.
Replace engine coolant temperature sensor.
CAUTION:
After repair or replacement of faulty parts, conduct
CLEAR MEMORY and INSPECTION MODES. [T3D0] and [T3E0].>
WIRING DIAGRAM:
OBD0174

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11. Diagnostics Chart with Trouble Code

OBD0199
J: DTC P0130
—FRONT OXYGEN SENSOR CIRCUIT
MALFUNCTION (FO2
—V)—
OBD0200A
DESCRIPTION:

The oxygen sensor is used to sense oxygen concentra-
tion in the exhaust gas. If the fuel ratio is leaner than the
stoichiometric ratio in the mixture (i.e. excessive amount of
air), the exhaust gas contains more oxygen. To the
contrary, if the fuel ratio is richer than the stoichiometric
ratio, the exhaust gas contains hardly any oxygen.

Therefore, examination of the oxygen concentration in
exhaust gas makes it possible to show whether the air/fuel
ratio is leaner or richer than the stoichiometric ratio.

The oxygen sensor has a zirconia tube (ceramic) which
generates voltage if there is a difference in oxygen concen-
tration between the inside and outside of the tube. Platinum
is coated on the inside and outside of the zirconia tube for
the purpose of catalysis and electrode provision. The hexa-
gon screw on the outside is grounded to the exhaust pipe,
and the inside is connected to the ECM through the har-
ness.

A ceramic heater is employed to improve performance at
low temperature.

When rich air-fuel mixture is burnt in the cylinder, the
oxygen in the exhaust gases reacts almost completely
through the catalytic action of the platinum coating on the
surface of the zirconia tube. This result is a very large dif-
ference in the oxygen concentration between the inside
and outside, and the electromotive force generated is
large.

When a lean air-fuel mixture is burnt in the cylinder,
oxygen remains in the exhaust gases even after the cata-
lytic action, and this results in a small difference in the
oxygen concentration. The electromotive force is very
small.
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11. Diagnostics Chart with Trouble Code

The difference in oxygen concentration changes greatly
in the vicinity of the optimum air-fuel ratio, and hence the
change in the electromotive force is also large. By inputting
this information into the MFI control module, the air-fuel
ratio of the supplied mixture can be determined easily. The
oxygen sensor does not generate much electromotive
force when the temperature is low. The characteristics of
the electromotive force stabilize at temperature of approxi-
mately 300 to 400°C (572 to 752°F).
DTC DETECTING CONDITION:

Two consecutive trips with fault
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11. Diagnostics Chart with Trouble Code

1.Check for other causes affecting exhaust gas.
2.Check front oxygen sensor data.
3.Check harness connector.
CAUTION:
After repair or replacement of faulty parts, conduct
CLEAR MEMORY and INSPECTION MODES. [T3D0] and [T3E0].>
WIRING DIAGRAM:

LHD model
OBD0201


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11. Diagnostics Chart with Trouble Code

OBD0145A
2
CHECK FRONT OXYGEN SENSOR DATA.
1) Turn ignition switch to OFF.
2) Connect the Subaru Select Monitor or the OBD-II gen-
eral scan tool to data link connector.
3) Start engine and Turn the Subaru Select Monitor and
the OBD-II general scan tool switch to ON.
4) Warm-up the engine until coolant temperature is above
70°C (160°F) and keep the engine speed at 2,000 rpm to
3,000 rpm for one minute.
5) Read data on Subaru Select Monitor or the OBD-II gen-
eral scan tool.
OBD0206
OBD0207

Subaru Select Monitor
Designate mode using function key.
Function mode: F14 or F15

F14: Front oxygen sensor max. output signal is indi-
cated.

F15: Front oxygen sensor min. output signal is indi-
cated.
: Is the difference of voltage between F14 and
F15 0.1 V, or less?
: Go to step 3.
: Replace front oxygen sensor.

OBD-II general scan tool
For detailed operation procedures, refer to the OBD-II Gen-
eral Scan Tool Instruction Manual.
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11. Diagnostics Chart with Trouble Code

OBD0705A
3
CHECK HARNESS CONNECTOR.
1) Turn ignition switch to OFF.
2) Disconnect connector from front oxygen sensor.
3) Turn ignition switch to ON.
4) Measure voltage between front oxygen sensor harness
connector and body.
: Connector & terminal
(B18) No. 4—Body/0.2 V, or more
: Repair harness and connector.
NOTE:
In this case, the following are the possible causes.

1Open circuit of harness between ECM and front oxygen
sensor.

2Poor contact in the ECM connector.
: Go to next.
: Is there poor contact in front oxygen sensor
connector?
: Repair poor contact in front oxygen sensor con-
nector.
: Replace front oxygen sensor.
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11. Diagnostics Chart with Trouble Code

OBD0209
K: DTC P0133
—FRONT OXYGEN SENSOR CIRCUIT SLOW
RESPONSE (FO2
—R)—
DESCRIPTION:
Refer to“J: DTC P0130—FRONT OXYGEN SENSOR
CIRCUIT MALFUNCTION—[T11J0]”.
DTC DETECTING CONDITION:

Two consecutive trips with fault
1.Check DTC P0130 on display.
No
Ye s

Inspect DTC P0130 using“11. Diagnostics Chart
with Trouble Code [T1100]”.

In this case, it is unnecessary to inspect DTC
P0133.
2.Check exhaust system.
CAUTION:
After repair or replacement of faulty parts, conduct
CLEAR MEMORY and INSPECTION MODES. [T3D0] and [T3E0].>

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11. Diagnostics Chart with Trouble Code

WIRING DIAGRAM:

RHD model
B2M0450
2
CHECK EXHAUST SYSTEM.
: Check the following.

Looseness of installation portion of front
exhaust pipe onto cylinder heads

Loosened connection of front exhaust
pipe and front catalytic converter

Damage of exhaust pipe which make a
hole
: Repair exhaust system.
: Replace front oxygen sensor.
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11. Diagnostics Chart with Trouble Code

OBD0212
L: DTC P0135
—FRONT OXYGEN SENSOR HEATER
CIRCUIT MALFUNCTION (FO2H)—
DESCRIPTION:
Refer to“J: DTC P0130—FRONT OXYGEN SENSOR
CIRCUIT MALFUNCTION—[T11J0]”.
DTC DETECTING CONDITION:

Two consecutive trips with fault
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2-7ON-BOARD DIAGNOSTICS II SYSTEM
11. Diagnostics Chart with Trouble Code