Subaru Impreza 3 / Impreza WRX / Impreza WRX STI. Service manual — part 606
AC(diag)-29
Diagnostic Procedure for Sensors
HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)
8. Diagnostic Procedure for Sensors
A: AMBIENT SENSOR
TROUBLE SYMPTOM:
• Fan speed is not switched when the fan dial is in AUTO position.
• Failure related to the ambient sensor is indicated in self-diagnosis.
WIRING DIAGRAM:
Air conditioning system, auto A/C model <Ref. to WI-77, AUTO A/C MODEL, WIRING DIAGRAM, Air Con-
Step
Check
Yes
No
1
CHECK AMBIENT SENSOR.
Perform the inspection of ambient sensor unit.
<Ref. to AC-45, INSPECTION, Ambient Sensor
(Auto A/C Model).>
Is the ambient sensor operating
properly?
Replace the ambi-
ent sensor. <Ref.
to AC-44,
REMOVAL, Ambi-
ent Sensor (Auto
A/C Model).>
2
CHECK INPUT SIGNAL FOR AMBIENT SEN-
SOR.
1) Turn the ignition to ON.
2) Measure the voltage between connector
(F78) terminals.
Connector & terminal
(F78) No. 2 (+) — No. 1 (–):
Is the voltage approx. 5 V?
I/F
*
1
*
2
B361
B361
1
7
2 3
4 5 6
8 9 10 11 12 13 14
i77
1 2 3 4 5 6 7 8 9 10
i3
5 6 7 8
2
1
9
4
3
10
24
22
23
25
27
26
28
11 12 13
14 15 16
17 18 19 20 21
F108
1
9
2 3
8
10
4
11 12 13 14 15 16
5 6 7
17 18
i77
*
1
*
2
*
1
*
2
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
i10
i88
2
1
i3
B38
i10
24
27
23
26
1 2
F78
2
1
F78
14
13
10
11
F108
B361
20
19
i88
AC-02343
AUTO A/C
CONTROL
MODULE
JOINT
CONNECTOR
AMBIENT
SENSOR
COMBINATION METER
MICRO COMPUTER
CAN TRANSCEIVER
& RECEIVER
CAN JOINT
CONNECTOR
: TERMINAL No. OPTIONAL ARRANGEMENT
AMONG 6, 7, 8, 9 AND 10
: TERMINAL No. OPTIONAL ARRANGEMENT
AMONG 1, 2, 3, 4 AND 5
AC(diag)-30
Diagnostic Procedure for Sensors
HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)
3
CHECK COMBINATION METER OUTPUT
SIGNAL.
1) Turn the ignition switch to OFF.
2) Pull out the combination meter.
3) Disconnect the connector from ambient
sensor.
4) Turn the ignition switch to ON.
5) Measure the voltage between the combina-
tion meter connector terminals.
Connector & terminal
(i10) No. 24 (+) — No. 23 (–):
Is the voltage approx. 5 V?
Replace the com-
bination meter.
<Ref. to IDI-16,
REMOVAL, Com-
bination Meter.>
4
CHECK HARNESS CONNECTOR BETWEEN
COMBINATION METER AND AMBIENT SEN-
SOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from the combi-
nation meter.
3) Measure the resistance of harness between
combination meter and ambient sensor.
Connector & terminal
(F78) No. 2 — (i10) No. 24:
Is the resistance less than 1 Ω? Go to step
Repair the open
circuit of the har-
ness between the
combination meter
and ambient sen-
sor.
5
CHECK HARNESS CONNECTOR BETWEEN
COMBINATION METER AND AMBIENT SEN-
SOR.
Measure the resistance of harness between
combination meter and ambient sensor.
Connector & terminal
(F78) No. 1 — (i10) No. 23:
Is the resistance less than 1 Ω? Replace the com-
bination meter.
<Ref. to IDI-16,
REMOVAL, Com-
bination Meter.>
Repair the open
circuit of the har-
ness between the
combination meter
and ambient sen-
sor.
6
CHECK HARNESS CONNECTOR BETWEEN
COMBINATION METER AND AUTO A/C
CONTROL MODULE.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from the combi-
nation meter.
3) Disconnect the auto A/C control module
connector.
4) Measure the resistance of harness between
the combination meter and auto A/C control
module.
Connector & terminal
(i88) No. 19 — (i10) No. 26:
Is the resistance less than 1 Ω? Go to step
7
CHECK HARNESS CONNECTOR BETWEEN
COMBINATION METER AND AUTO A/C
CONTROL MODULE.
Measure the resistance of harness between the
combination meter and auto A/C control mod-
ule.
Connector & terminal
(i88) No. 20 — (i10) No. 27:
Is the resistance less than 1 Ω? Go to step
8
CHECK FOR POOR CONTACT.
Check poor contact of auto A/C control module
connector.
Is there poor contact of connec-
tor?
Repair the connec-
tor.
Replace the auto
A/C control mod-
ule. <Ref. to AC-
31, REMOVAL,
Control Unit (Auto
A/C Model).>
Step
Check
Yes
No
AC(diag)-31
Diagnostic Procedure for Sensors
HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)
B: IN-VEHICLE SENSOR
TROUBLE SYMPTOM:
• Blower fan speed, air flow outlet and FRESH/RECIRC do not change after turning the AUTO switch to ON.
• Failure related to the in-vehicle sensor is indicated in self-diagnosis.
WIRING DIAGRAM:
Air conditioning system, auto A/C model <Ref. to WI-77, AUTO A/C MODEL, WIRING DIAGRAM, Air Con-
Step
Check
Yes
No
1
CHECK IN-VEHICLE SENSOR.
Perform the inspection of in-vehicle sensor unit.
<Ref. to AC-48, INSPECTION, In-Vehicle Sen-
sor (Auto A/C Model).>
Is the in-vehicle sensor nor-
mal?
Replace the in-
vehicle sensor.
<Ref. to AC-47,
REMOVAL, In-
Vehicle Sensor
(Auto A/C Model).>
2
CHECK INPUT SIGNAL FOR IN-VEHICLE
SENSOR.
1) Turn the ignition switch to ON.
2) Measure the voltage between in-vehicle
sensor harness connector terminals.
Connector & terminal
(i55) No. 2 (+) — No. 1 (–):
Is the voltage approx. 5 V?
3
CHECK AUTO A/C CONTROL MODULE
OUTPUT SIGNAL.
1) Turn the ignition switch to OFF.
2) Remove the auto A/C control module.
3) Turn the ignition switch to ON.
4) Measure the voltage between connector
terminals of auto A/C control module.
Connector & terminal
(i88) No. 17 (+) — (i88) No. 14 (–):
Is the voltage approx. 5 V?
AC-01700
i88
17
14
i55
1
2
i55
1 2
i88
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
AUTO A/C
CONTROL
MODULE
IN-VEHICLE
SENSOR
AC(diag)-32
Diagnostic Procedure for Sensors
HVAC SYSTEM (AUTO A/C) (DIAGNOSTICS)
4
CHECK HARNESS BETWEEN AUTO A/C
CONTROL MODULE AND IN-VEHICLE SEN-
SOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from the auto A/C
control module.
3) Measure the resistance of harness between
auto A/C control module and in-vehicle sensor.
Connector & terminal
(i55) No. 2 — (i88) No. 17:
Is the resistance less than 1 Ω? Go to step
Repair the harness
between auto A/C
control module and
in-vehicle sensor.
5
CHECK HARNESS BETWEEN AUTO A/C
CONTROL MODULE AND IN-VEHICLE SEN-
SOR.
Measure the resistance of harness between
auto A/C control module and in-vehicle sensor.
Connector & terminal
(i55) No. 1 — (i88) No. 14:
Is the resistance less than 1 Ω? Go to step
Repair the harness
between auto A/C
control module and
in-vehicle sensor.
6
CHECK FOR POOR CONTACT.
Check poor contact of auto A/C control module
connector.
Is there poor contact of connec-
tor?
Repair the connec-
tor.
Replace the auto
A/C control mod-
ule. <Ref. to AC-
31, REMOVAL,
Control Unit (Auto
A/C Model).>
Step
Check
Yes
No
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