Subaru 2004 LEGACY Service Manual page 53

Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTICS)
Step
1 CHECK CURRENT DATA.
1) Start the engine.
2) Read the data of mass air flow and intake
air temperature sensor signal using Subaru
Select Monitor or OBD-II general scan tool.
NOTE:
• Subaru Select Monitor
For detailed operation procedures, refer to the
"READ CURRENT DATA SHOWN ON DIS-
PLAY FOR ENGINE". <Ref. to
EN(H6DO)(diag)-25, Subaru Select Monitor.>
• OBD-II general scan tool
For detailed operation procedures, refer to the
OBD-II General Scan Tool Operation Manual.
2 CHECK HARNESS BETWEEN MASS AIR
FLOW AND INTAKE AIR TEMPERATURE
SENSOR AND ECM CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector mass air flow and
intake air temperature sensor.
3) Measure the voltage between mass air flow
and intake air temperature sensor connector
and engine ground.
Connector & terminal
(B3) No. 4 (+) — Engine ground (
3 CHECK HARNESS BETWEEN MASS AIR
FLOW AND INTAKE AIR TEMPERATURE
SENSOR AND ECM CONNECTOR.
1) Turn the ignition switch to ON.
2) Measure the voltage between mass air flow
and intake air temperature sensor connector
and engine ground.
Connector & terminal
(B3) No. 4 (+) — Engine ground (
4 CHECK HARNESS BETWEEN MASS AIR
FLOW AND INTAKE AIR TEMPERATURE
SENSOR AND ECM CONNECTOR.
Measure the voltage between mass air flow
and intake air temperature sensor connector
and engine ground.
Connector & terminal
(B3) No. 4 (+) — Engine ground (
Check
Is the intake air temperature
less than −40°C (−40°F)?
Is the voltage more than 10 V? Repair the battery
−
):
Is the voltage more than 10 V? Repair the battery
−
):
Is the voltage more than 3 V?
−
):
EN(H6DO)(diag)-122
Yes
Go to step 2. Repair the poor
contact.
NOTE:
In this case repair
the following:
• Poor contact in
mass air flow and
intake air tempera-
ture sensor
• Poor contact in
ECM
• Poor contact in
coupling connector
• Poor contact in
joint connector
Go to step 3.
short circuit in har-
ness between
mass air flow and
intake air tempera-
ture sensor and
ECM connector.
Go to step 4.
short circuit in har-
ness between
mass air flow and
intake air tempera-
ture sensor and
ECM connector.
Go to step 5. Repair the har-
ness and connec-
tor.
NOTE:
In this case repair
the following:
• Open circuit in
harness between
mass air flow and
intake air tempera-
ture sensor and
ECM connector
• Poor contact in
mass air flow and
intake air tempera-
ture sensor
• Poor contact in
ECM
• Poor contact in
coupling connector
• Poor contact in
joint connector
No