SUBARU LEGACY 1995 Service Repair Manual

OBD0700A
3CHECK HARNESS CONNECTOR BETWEEN
ECM AND THROTTLE POSITION SENSOR.
1) Turn ignition switch to OFF.
2) Disconnect connectors from throttle position sensor.
3) Turn ignition switch to ON.
4) Measure voltage between throttle position sensor con-
nector and body.
: Connector & terminal
(E13) No. 3—Body/4.5 V, or more
: Repair harness and connector.
NOTE:
In this case, the possible causes are:

1Open circuit of the harness between connector (E13)
terminal No. 3 and connector (B84) terminal No. 22, or
the following:

2Poor contact in throttle position sensor connector

3Poor contact in ECM connector

4Poor contact in coupling connector (B21)
: Go to the next step.
OBD0701A
5) Turn ignition switch to OFF.
6) Measure resistance of harness between ECM connec-
tor and throttle position sensor connector.
: Connector & terminal
(B84) No. 24—(E13) No. 2/10Ω, or less
: Repair harness and connector.
NOTE:
In this case, the following are the possible causes.

1Open circuit between connector (B84) terminal No. 24
and connector (E13) terminal No. 2.

2Poor contact in ECM connector.

3Poor contact in throttle position sensor connector

4Poor contact in coupling connector (B21)
: Go to next step.
165
2-7ON-BOARD DIAGNOSTICS II SYSTEM
11. Diagnostics Chart with Trouble Code

OBD0702A
7) Measure resistance of harness between throttle posi-
tion sensor connector and body.
: Connector & terminal
(E13) No. 2—Body/10Ω, or less
: Repair short circuit of harness between throttle
position sensor and ECM connector.
: Go to next.
: Is there poor contact in throttle position
sensor connector?
: Repair poor contact in throttle position sensor
connector.
: Replace throttle position sensor.
OBD0703A
4CHECK HARNESS CONNECTOR BETWEEN
THROTTLE POSITION SENSOR AND BODY.
1) Turn ignition switch to OFF.
2) Disconnect connector from throttle position sensor.
3) Measure resistance of harness between throttle posi-
tion sensor connector and body.
: Connector & terminal
(E13) No. 1—Body/10Ω, or less
: Repair open circuit of harness between throttle
position sensor and ECM connector.
: Go to the next step.
OBD0704A
4) Turn ignition switch to ON.
5) Measure voltage between throttle position sensor con-
nector and body.
: Connector & terminal
(E13) No. 2—Body/4.9 V, or more
: Repair short circuit of harness between throttle
position sensor and ECM connector.
: Replace throttle position sensor.
166
2-7ON-BOARD DIAGNOSTICS II SYSTEM
11. Diagnostics Chart with Trouble Code

OBD0189
H: DTC P0121
—THROTTLE POSITION SENSOR CIRCUIT
RANGE/PERFORMANCE PROBLEM (TH
—R)
—
DESCRIPTION:
Refer to“G: DTC P0120—THROTTLE POSITION SEN-
SOR CIRCUIT MALFUNCTION—[T11G0]”.
DTC DETECTING CONDITION:

Two consecutive trips with fault
TROUBLE SYMPTOM:

Erroneous idling

Engine stalls.

Poor driving performance
167
2-7ON-BOARD DIAGNOSTICS II SYSTEM
11. Diagnostics Chart with Trouble Code

Check DTC P0120 on display.
No
Ye s

Inspect DTC P0120 using“11. Diagnostics Chart
with Trouble Code [T1100]”.

In this case, it is unnecessary to inspect DTC
P0121.
Replace throttle position sensor.
CAUTION:
After repair or replacement of faulty parts, conduct
CLEAR MEMORY and INSPECTION MODES. <Ref. to
[T3D0] and [T3E0].>
WIRING DIAGRAM:
OBD0183

168
2-7ON-BOARD DIAGNOSTICS II SYSTEM
11. Diagnostics Chart with Trouble Code

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.
169
2-7ON-BOARD DIAGNOSTICS II SYSTEM
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. <Ref. to
[T3D0] and [T3E0].>
WIRING DIAGRAM:
OBD0174

170
2-7ON-BOARD DIAGNOSTICS II SYSTEM
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.
171
2-7ON-BOARD DIAGNOSTICS II SYSTEM
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
172
2-7ON-BOARD DIAGNOSTICS II SYSTEM
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. <Ref. to
[T3D0] and [T3E0].>
WIRING DIAGRAM:

LHD model
OBD0201


173
2-7ON-BOARD DIAGNOSTICS II SYSTEM
11. Diagnostics Chart with Trouble Code

WIRING DIAGRAM:

RHD model
B2M0450
1CHECK FOR OTHER CAUSES AFFECTING
EXHAUST GAS.
: Is CO % more than 2 % after engine warm-
up?
: Check fuel system.
NOTE:
Check for use of improper fuel.
Check if engine oil or coolant level is extremely low.
: Go to step 2.
174
2-7ON-BOARD DIAGNOSTICS II SYSTEM
11. Diagnostics Chart with Trouble Code