SUBARU LEGACY 1995 Service Repair Manual

OBD0142
B: DTC P0100
—MASS AIR FLOW SENSOR CIRCUIT
MALFUNCTION (QA)—
OBD0143A
DESCRIPTION:

The MFI system employs a hot film type air flow sensor.
These mass air flow sensors convert the amount of air
taken into the engine into an electric signal by utilizing the
heat transfer phenomenon between the incoming air and a
heating resistor (hot film) located in the air intake.

The features of these flow sensor types are as follows:
1) High-altitude compensation is made automatically.
2) Quick response
3) These are no moving parts.
4) They are compact.
DTC DETECTING CONDITION:

Immediately at fault recognition
TROUBLE SYMPTOM:

Erroneous idling

Engine stalls.

Poor driving performance
135
2-7ON-BOARD DIAGNOSTICS II SYSTEM
11. Diagnostics Chart with Trouble Code

1.Connect Subaru Select Monitor or the OBD-
II general scan tool, and read data.5.Check harness.
2.Check input signal for ECM. (Using voltage
meter and Subaru Select Monitor.)
3.Check power supply to mass air flow
sensor.
4.Check harness connector between ECM and
mass air flow sensor.
CAUTION:
After repair or replacement of faulty parts, conduct
CLEAR MEMORY and INSPECTION MODES. [T3D0] and [T3E0].>
WIRING DIAGRAM:

LHD model
OBD0144



136
2-7ON-BOARD DIAGNOSTICS II SYSTEM
11. Diagnostics Chart with Trouble Code

WIRING DIAGRAM:

RHD model
B2M0448
137
2-7ON-BOARD DIAGNOSTICS II SYSTEM
11. Diagnostics Chart with Trouble Code

OBD0145A
B2M0271
OBD0616
1CONNECT SUBARU SELECT MONITOR OR
THE OBD-II GENERAL SCAN TOOL, AND
READ DATA.
1) Turn ignition switch to OFF.
2) Connect Subaru Select Monitor or the OBD-II general
scan tool to data link connector.
3) Turn ignition switch to ON and Subaru Select Monitor or
the OBD-II general scan tool switch to ON.
4) Start engine.
5) Read data on Subaru Select Monitor or OBD-II general
scan tool.

Subaru Select Monitor
Designate mode using function key.
Function mode: F08 or F47

F08: Voltage input from mass air flow sensor is shown
on display.

F47: Mass air flow is shown on display.

F08: Is sensor output equal to or more
than 0.3 V and equal to or less than
5.0 V?

F47: Is sensor output equal to or more
than 1.3 g/sec and equal to or less
than 250 g/sec?
Probable cause: Poor connect of connectors, circuit and
grounding line.
: Even if MIL lights up, the circuit has returned to a
normal condition at this time. A temporary poor
contact of the connector or harness may be the
cause. Repair harness or connector of the mass
air flow sensor.
HINT:
1Open or short circuit between mass air flow sen-
sor and ECM.

2Poor contact of connectors for mass air flow sen-
sor or ECM.
: Go to next.
: Is the value less than 0.3 V (1.3 g/sec)?
: Go to step 2.
: Go to step 5.

OBD-II general scan tool
For detailed operation procedures, refer to the OBD-II Gen-
eral Scan Tool Instruction Manual.
138
2-7ON-BOARD DIAGNOSTICS II SYSTEM
11. Diagnostics Chart with Trouble Code

OBD0689A
2CHECK INPUT SIGNAL FOR ECM. (USING
VOLTAGE METER AND SUBARU SELECT
MONITOR.)
Measure voltage between ECM and body while engine is
idling.
: Connector & terminal
(B84) No. 26—Body/0.3 V, or less
: Go to step 3.
: Go to next.
G2M0527
: Is the voltage more than 0.3 V while shaking
harness and connector of ECM and monitor-
ing the value with Subaru select monitor?
: Repair poor contact in ECM connector.
: Replace ECM with a new one.
B2M0623A
3CHECK POWER SUPPLY TO MASS AIR
FLOW SENSOR.
1) Turn ignition switch to OFF.
2) Disconnect connector from mass air flow sensor.
3) Turn ignition switch to ON.
4) Measure voltage between mass air flow sensor connec-
tor and body.
: Connector & terminal
(B3) No. 1—Body/10 V, or more
: Go to step 4.
: Repair open circuit of harness between main relay
connector and mass air flow sensor connector.
139
2-7ON-BOARD DIAGNOSTICS II SYSTEM
11. Diagnostics Chart with Trouble Code

OBD0690A
4CHECK HARNESS CONNECTOR BETWEEN
ECM AND MASS AIR FLOW SENSOR.
1) Turn ignition switch to OFF.
2) Disconnect connector from ECM.
3) Measure resistance of harness connector between
ECM and mass air flow sensor.
: Connector & terminal

1(B84) No. 26—(B3) No. 4/10Ω, or less

2(B84) No. 46—(B3) No. 3/10Ω, or less

3(B84) No. 25—(B3) No. 2/10Ω, or less
: Replace mass air flow sensor with a new one.
: Repair poor contact and open circuit of harness
between ECM and mass air flow sensor connec-
tor.
G2M0527
5
CHECK HARNESS.
1) Turn ignition switch to OFF.
2) Disconnect connector from mass air flow sensor.
3) Connect Subaru Select Monitor or OBD-II General
Scan Tool to data link connector.
4) Turn ignition switch to ON.
5) Read data on Subaru select monitor or OBD-II general
scan tool.

Subaru Select Monitor
Designate mode using function key.
Function mode: F08
: Is the value more than 5 V?
: Repair short circuit of harness between mass air
flow sensor and ECM.
: Go to next.
: Is there poor contact in mass air flow sensor
connector?
: Repair poor contact in mass air flow sensor con-
nector.
: Replace mass air flow sensor.

OBD-II general scan tool
For detailed operation procedures, refer to OBD-II General
Scan Tool Instruction Manual.
140
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11. Diagnostics Chart with Trouble Code

OBD0152
C: DTC P0101
—MASS AIR FLOW SENSOR CIRCUIT
RANGE/PERFORMANCE PROBLEM (QA
—R)
—
DESCRIPTION:
Refer to“B: DTC P0100—MASS AIR FLOW SENSOR
CIRCUIT MALFUNCTION—[T11B0]”.
DTC DETECTING CONDITION:

Two consecutive trips with fault
TROUBLE SYMPTOM:

Erroneous idling

Engine stalls.

Poor driving performance
141
2-7ON-BOARD DIAGNOSTICS II SYSTEM
11. Diagnostics Chart with Trouble Code

1.Check DTC P0100 on display.
No
Ye s

Inspect DTC P0100 using“11. Diagnostics
Chart with Trouble Code [T1100]”.

In this case, it is unnecessary to inspect DTC
P0101.
Replace mass air flow sensor.
CAUTION:
After repair or replacement of faulty parts, conduct
CLEAR MEMORY and INSPECTION MODES. [T3D0] and [T3E0].>
WIRING DIAGRAM:

LHD model
OBD0144

142
2-7ON-BOARD DIAGNOSTICS II SYSTEM
11. Diagnostics Chart with Trouble Code

WIRING DIAGRAM:

RHD model
B2M0448
143
2-7ON-BOARD DIAGNOSTICS II SYSTEM
11. Diagnostics Chart with Trouble Code

OBD0154
D: DTC P0105
—PRESSURE SENSOR CIRCUIT
MALFUNCTION (P
—S)—
OBD0155A
DESCRIPTION:
The pressure sensor is used in AT vehicles. It is located in
the engine compartment, at the front of the right-hand sus-
pension. It consists of a solenoid, which switches between
the atmospheric pressure and suction pressure lines and a
pressure sensor. This arrangement allows either pressure
line to be monitored.
A sensor output signal is sent to the ECM to diagnose the
EGR system and evaporative emission control system.
(The pressure sensor is not used in MT vehicles.)
DTC DETECTING CONDITION:

Immediately at fault recognition
144
2-7ON-BOARD DIAGNOSTICS II SYSTEM
11. Diagnostics Chart with Trouble Code