Subaru Legacy IV (2008 year). Service manual - part 287

CO(H4DOTC)-10

Radiator Fan System

COOLING

DIAGNOSIS:
Radiator main fan and radiator sub fans do not rotate under the above operating conditions.

Step

Check

Yes

No

1

CHECK OPERATION OF RADIATOR FAN.
1) Connect the delivery (test) mode connector.
2) Turn the ignition switch to ON.
3) Using the Subaru Select Monitor, check the 
forced operation of the radiator fan relay.

NOTE:
• When performing a forced operation radiator
fan relay check using the Subaru Select Moni-
tor, the radiator main fan and radiator sub fan
will repeat low speed revolution 

o high speed

revolution 

o OFF in this order.

• Subaru Select Monitor
Refer to “Compulsory Valve Operation Check
Mode” for detailed procedures. 
<Ref. to EN(H4DOTC)(diag)-53, Compulsory
Valve Operation Check Mode.>

Do the radiator main fans and 
radiator sub fans rotate at low 
speed?

Go to step 2.

Go to step 3.

2

CHECK OPERATION OF RADIATOR FAN.
1) Connect the delivery (test) mode connector.
2) Turn the ignition switch to ON.
3) Perform the compulsory operation check for 
the radiator fan relay using Subaru Select Mon-
itor.

NOTE:
• When performing a forced operation radiator
fan relay check using the Subaru Select Moni-
tor, the radiator main fan and radiator sub fan
will repeat low speed revolution 

o high speed

revolution 

o OFF in this order.

• Subaru Select Monitor
Refer to “Compulsory Valve Operation Check
Mode” for detailed procedures. 
<Ref. to EN(H4DOTC)(diag)-53, Compulsory
Valve Operation Check Mode.>

Do the radiator main fans and 
radiator sub fans rotate at high 
speed?

Radiator main fan 
system is normal.

Go to step 27.

3

CHECK POWER SUPPLY TO SUB FAN RE-
LAY.
1) Turn the ignition switch to OFF.
2) Remove the sub fan relay from the relay 
holder.
3) Measure the voltage between the sub fan 
relay terminal and chassis ground.

Connector & terminal

(F27) No. 10 (+) — Chassis ground (–):

Is the voltage 10 V or more?

Go to step 4.

Go to step 5.

4

CHECK POWER SUPPLY TO SUB FAN RE-
LAY.
1) Turn the ignition switch to ON.
2) Measure the voltage between the sub fan 
relay terminal and chassis ground.

Connector & terminal

(F27) No. 13 (+) — Chassis ground (–):

Is the voltage 10 V or more?

Go to step 7.

Go to step 6.

5

CHECK FUSE.
1) Turn the ignition switch to OFF.
2) Remove the fuse No. 3.
3) Check the condition of fuse.

Is the fuse blown out?

Replace the fuse.

Repair the power 
supply line.

6

CHECK FUSE.
1) Turn the ignition switch to OFF.
2) Remove the fuse No. 22.
3) Check the condition of fuse.

Is the fuse blown out?

Replace the fuse.

Repair the power 
supply line.

CO(H4DOTC)-11

Radiator Fan System

COOLING

7

CHECK SUB FAN RELAY.
1) Turn the ignition switch to OFF.
2) Measure the resistance between sub fan 
relay terminals.

Terminals

No. 10 — No. 11:

Is the resistance 1 M

: or 

more?

Go to step 8.

Replace the sub 
fan relay.

8

CHECK SUB FAN RELAY.
1) Connect the battery to terminals No. 12 and 
No. 13 of the sub fan relay.
2) Measure the resistance between sub fan 
relay terminals.

Terminals

No. 10 — No. 11:

Is the resistance less than 1 

:? Go to step 9.

Replace the sub 
fan relay.

9

CHECK HARNESS BETWEEN SUB FAN RE-
LAY TERMINAL AND SUB FAN MOTOR 
CONNECTOR.
1) Disconnect the connector from the sub fan 
motor.
2) Measure the resistance of harness between 
the sub fan relay terminal and sub fan motor 
connector.

Connector & terminal

(F16) No. 1 — (F27) No. 11:

Is the resistance less than 1 

:? Go to step 10.

Repair the open 
circuit of harness 
between sub fan 
relay terminal and 
sub fan motor con-
nector.

10

CHECK HARNESS BETWEEN SUB FAN MO-
TOR CONNECTOR AND MAIN FAN RELAY 2 
CONNECTOR.
1) Remove main fan relay 2 from the relay 
holder.
2) Measure the resistance of harness between 
sub fan motor connector and main fan relay 2 
connector.

Connector & terminal

(F16) No. 2 — (F27) No. 18:

Is the resistance less than 1 

:? Go to step 11.

Repair the open 
circuit of the har-
ness between sub 
fan motor connec-
tor and main fan 
relay 2 connector.

11

CHECK POOR CONTACT.
Check poor contact of sub fan motor connector.

Is there poor contact in the sub 
fan motor connector?

Repair the poor 
contact of sub fan 
motor connector.

Go to step 12.

12

CHECK SUB FAN MOTOR.
Connect the battery positive (+) terminal to ter-
minal No. 1 of the sub fan motor, and the ground 
(–) terminal to terminal No. 2.

Does the radiator sub fan 
rotate?

Go to step 13.

Replace the sub 
fan motor.

13

CHECK MAIN FAN RELAY 2.
Measure the resistance of main fan relay 2.

Terminals

No. 21 — No. 18:

Is the resistance less than 1 

:? Go to step 14.

Replace the main 
fan relay 2.

14

CHECK HARNESS BETWEEN MAIN FAN 
RELAY 2 AND MAIN FAN MOTOR CONNEC-
TOR.
1) Disconnect the connector from the main fan 
motor.
2) Measure the resistance of the harness 
between main fan relay 2 terminal and main fan 
motor connector.

Connector & terminal

(F17) No. 1 — (F27) No. 2:

Is the resistance less than 1 

:? Go to step 15.

Repair the open 
circuit of the har-
ness between 
main fan relay 2 
terminal and main 
fan motor connec-
tor.

Step

Check

Yes

No

CO(H4DOTC)-12

Radiator Fan System

COOLING

15

CHECK MAIN FAN MOTOR AND GROUND 
CIRCUIT.
Measure the resistance between main fan 
motor connector and chassis ground.

Connector & terminal

(F17) No. 2 — Chassis ground:

Is the resistance less than 5 

:? Go to step 16.

Repair the open 
circuit of the har-
ness between 
main fan motor 
connector and 
chassis ground.

16

CHECK POOR CONTACT.
Check poor contact of main fan motor connec-
tor.

Is there poor contact in the 
main fan motor connector?

Repair the poor 
contact of main fan 
motor connector.

Go to step 17.

17

CHECK MAIN FAN MOTOR.
Connect the battery positive (+) terminal to ter-
minal No. 1 of the main fan motor, and the 
ground (–) terminal to terminal No. 2.

Does the radiator main fan 
rotate?

Go to step 18.

Replace the main 
fan motor.

18

CHECK HARNESS BETWEEN SUB FAN RE-
LAY AND ECM.
1) Disconnect the connectors from ECM.
2) Measure the resistance between the sub 
fan relay terminal and ECM connector.

Connector & terminal

(B136) No. 18 — (F27) No. 12:

Is the resistance less than 1 

:? Go to step 19.

Repair the open 
circuit of harness 
between sub fan 
relay terminal and 
ECM.

19

CHECK POOR CONTACT.
Check for poor contact of the ECM connector.

Is there poor contact in ECM 
connector?

Repair the poor 
contact of ECM 
connector.

Check the DTC. 
Repair the trouble 
cause. <Ref. to 
EN(H4DOTC)(diag
)-42, Read Diag-
nostic Trouble 
Code (DTC).>

20

CHECK MAIN FAN RELAY 1.
1) Turn the ignition switch to OFF.
2) Remove main fan relay 1 from the main fuse 
box.
3) Measure the resistance of terminal in main 
fan relay 1 switch.

Is the resistance 1 M

: or 

more?

Go to step 21.

Replace the main 
fan relay 1.

21

CHECK MAIN FAN RELAY 1.
1) Connect the main fan relay 1 coil side termi-
nal to the battery.
2) Measure the resistance between terminals 
of main fan relay 1 switch.

Is the resistance less than 1 

:? Go to step 22.

Replace the main 
fan relay 1.

22

CHECK HARNESS BETWEEN MAIN FAN 
RELAY 1 AND MAIN FAN MOTOR CONNEC-
TOR.
1) Disconnect the connector from the main fan 
motor.
2) Measure the resistance of the harness 
between main fan relay 1 terminal and main fan 
motor connector.

Connector & terminal

(F17) No. 1 — (F36) No. 6:

Is the resistance less than 1 

:? Go to step 23.

Repair the open 
circuit of the har-
ness between 
main fan relay 1 
terminal and main 
fan motor connec-
tor.

23

CHECK HARNESS BETWEEN MAIN FAN 
RELAY 1 AND ECM.
1) Disconnect the connectors from ECM.
2) Measure the resistance between main fan 
relay 1 terminal and ECM connector.

Connector & terminal

(B136) No. 29 — (B143) No. 7:

Is the resistance less than 1 

:? Go to step 24.

Repair the open 
circuit of the har-
ness between 
main fan relay 1 
terminal and ECM.

Step

Check

Yes

No

CO(H4DOTC)-13

Radiator Fan System

COOLING

24

CHECK HARNESS BETWEEN MAIN FAN 
RELAY 2 AND ECM.
Measure the resistance between main fan relay 
2 terminal and ECM connector.

Connector & terminal

(B136) No. 29 — (F27) No. 22:

Is the resistance less than 1 

:? Go to step 25.

Repair the open 
circuit of the har-
ness between 
main fan relay 2 
terminal and ECM.

25

CHECK FUSE.
1) Turn the ignition switch to OFF.
2) Remove the fuse No. 4 and 26.
3) Check the condition of fuse.

Is the fuse blown out?

Replace the fuse.

Go to step 26.

26

CHECK POOR CONTACT.
Check for poor contact of the ECM connector.

Is there poor contact in ECM 
connector?

Repair the poor 
contact of ECM 
connector.

Repair the power 
supply circuit to the 
main fuse box.

27

CHECK OPERATION OF RADIATOR FAN.
If the both fans do not rotate at high speed in the 
condition of step 2, check whether the radiator 
sub fan is rotating.

Does the radiator sub fan 
rotate?

Go to step 20.

Go to step 28.

28

CHECK GROUND CIRCUIT OF MAIN FAN 
RELAY 2.
1) Remove the main fan relay 2 from the relay 
holder.
2) Measure the resistance between main fan 
relay 2 terminal and chassis ground.

Connector & terminal

(F27) No. 19 — Chassis ground:

Is the resistance less than 1 

:? Go to step 29.

Repair the open 
circuit of harness 
between main fan 
relay 2 and chassis 
ground.

29

CHECK POWER SUPPLY TO MAIN FAN RE-
LAY 2.
1) Turn the ignition switch to ON.
2) Measure the voltage between main fan relay 
2 terminal and chassis ground.

Connector & terminal

(F27) No. 20 (+) — Chassis ground (–):

Is the voltage 10 V or more?

Go to step 30.

Repair the power 
supply line.

30

CHECK MAIN FAN RELAY 2.
1) Turn the ignition switch to OFF.
2) Remove the main fan relay 2.
3) Measure the resistance of main fan relay 2.

Terminals

(F27) No. 18 — (F27) No. 19:

Is the resistance 1 M

: or 

more?

Go to step 31.

Replace the main 
fan relay 2.

31

CHECK MAIN FAN RELAY 2.
1) Connect the battery to terminals No. 20 and 
No. 22 of the main fan relay 2.
2) Measure the resistance of main fan relay 2.

Terminals

(F27) No. 18 — (F27) No. 19:

Is the resistance less than 1 

:? Go to step 23.

Replace the main 
fan relay 2.

Step

Check

Yes

No