Subaru Legacy III (2000-2003 year). Manual — part 578

AT-46

AUTOMATIC TRANSMISSION (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

B: DTC 23 MASS AIR FLOW SIGNAL (TURBO MODEL)

DIAGNOSIS:
The input signal circuit of TCM from ECM is open or shorted.
TROUBLE SYMPTOM:
Excessive shift shock.
WIRING DIAGRAM:

Step

Value

Yes

No

1

CHECK ENGINE GROUND TERMINALS AND
GROUND CIRCUIT OF ECM.
<Ref. to AT-52, DTC 31 THROTTLE POSI-
TION SENSOR, Diagnostic Procedure with
Diagnostic Trouble Code (DTC).>
Is there any trouble?

There is a trouble.

Repair the ground
terminal and/or
ground circuit of
ECM.

Go to step 2.

2

CHECK HARNESS CONNECTOR BETWEEN
TCM AND ECM.
1) Turn the ignition switch to OFF.
2) Disconnect the connectors from TCM and

ECM.

3) Measure the resistance of harness

between TCM and ECM connector.

Connector & terminal

(B54) No. 1 — (B135) No. 28:

Is the measured value less than the speci-
fied value?

1

Ω

Go to step 3.

Repair the open
circuit in harness
between TCM and
ECM connector.

AT-00574

28

1

B54

B54

B135 ECM

TCM

1

2

3

4

5

6

7

8

9

10 11 12 13 14 15

16

17

18

19 20 21

22 23

24

B135

5 6

7 8

2

1

9

4

3

10

24

22

23

25

11 12 13 14 15

26 27 28

16 17 18 19

20 21

AT-47

AUTOMATIC TRANSMISSION (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

3

CHECK HARNESS CONNECTOR BETWEEN
TCM AND ECM.
Measure the resistance of harness between
TCM connector and chassis ground.

Connector & terminal

(B54) No. 1 — Chassis ground:

Does the measured value exceed the specified
value?

1 M

Ω

Go to step 4.

Repair the short
circuit in harness
between TCM and
ECM connector.

4

PREPARE SUBARU SELECT MONITOR.
Do you have a Subaru Select Monitor?

Subaru Select Monitor is avail-
able.

Go to step 6.

Go to step 5.

5

CHECK INPUT SIGNAL FOR TCM.
1) Connect the connectors to TCM and ECM.
2) Start the engine and warm-up the transmis-

sion until ATF temperature is above 80

°

C

(176

°

F).

NOTE:

If ambient temperature is below 0

°

C (32

°

F),

drive the vehicle until ATF reaches its operating
temperature.

3) Idle the engine.
4) Measure the voltage between TCM con-

nector and chassis ground.

Connector & terminal

(B54) No. 1 (+) — Chassis ground (

−−−−

):

Is the measured value within the specified
range?

0.9 — 1.4 V

Even if the power
indicator light
lights up, the cir-
cuit has returned
to a normal condi-
tion at this time. A
temporary poor
contact of the con-
nector or harness
may be the cause.
Repair harness or
connector in the
TCM and ECM.

Go to step 7.

6

CHECK INPUT SIGNAL FOR TCM USING
SUBARU SELECT MONITOR.
1) Connect the connectors to TCM and ECM.
2) Connect the Subaru Select Monitor to data

link connector.

3) Start the engine and turn the Subaru Select

Monitor switch to ON.

4) Warm-up the engine until engine coolant

temperature is above 80

°

C (176

°

F).

5) Idle the engine.
6) Read the data of mass air flow sensor sig-

nal using Subaru Select Monitor.

•Display shows the mass air flow sensor signal
value sent from ECM.

Is the data of mass air flow sensor within
the specified range?

0.9 — 1.4 V

Even if the power
indicator light
lights up, the cir-
cuit has returned
to a normal condi-
tion at this time. A
temporary poor
contact of the con-
nector or harness
may be the cause.
Repair harness or
connector in the
TCM and ECM.

Go to step 7.

7

CHECK POOR CONTACT.
Is there poor contact in mass air flow sensor
signal circuit?

There is poor contact.

Repair the poor
contact.

Replace TCM.
<Ref. to AT-76,
Transmission Con-
trol Module
(TCM).>

Step

Value

Yes

No

AT-48

AUTOMATIC TRANSMISSION (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

C: DTC 27 ATF TEMPERATURE SENSOR

DIAGNOSIS:
Input signal circuit of TCM to ATF temperature sensor is open or shorted.
TROUBLE SYMPTOM:
Excessive shift shock.
WIRING DIAGRAM:

AT-00776

11

20

11

12

A

TF TEMPERA

TURE

SENSOR

B54

B11

T4

TCM

B11

TRANSMISSION

1 2

5

6 7

8

13

14 15

16

9 10

11 12

3 4

17 18

19 20

B54

1 2 3 4

10 11 12
19 20 21

13

5 6

14 15

7

8

9

16

17

18

22

23

24

AT-49

AUTOMATIC TRANSMISSION (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

Step

Value

Yes

No

1

CHECK HARNESS CONNECTOR BETWEEN
TCM AND ATF TEMPERATURE SENSOR.
1) Turn ignition switch to OFF.
2) Disconnect connector from transmission

and TCM.

3) Measure resistance of harness between

TCM and transmission connector.

Connector & terminal

(B54) No. 20 — (B11) No. 12:

Is the measured value less than the speci-
fied value?

1

Ω

Go to step 2.

Repair open circuit
in harness
between TCM and
transmission con-
nector.

2

CHECK HARNESS CONNECTOR BETWEEN
TCM AND ATF TEMPERATURE SENSOR.
Measure resistance of harness between TCM
and transmission connector.

Connector & terminal

(B54) No. 11 — (B11) No. 11:

Is the measured value less than the specified
value?

1

Ω

Go to step 3.

Repair open circuit
in harness
between TCM and
transmission con-
nector.

3

CHECK HARNESS CONNECTOR BETWEEN
TCM AND ATF TEMPERATURE SENSOR.
Measure resistance of harness between TCM
connector and chassis ground.

Connector & terminal

(B54) No. 20 — Chassis ground:

Does the measured value exceed the specified
value?

1 M

Ω

Go to step 4.

Repair short circuit
in harness
between TCM and
transmission con-
nector.

4

CHECK HARNESS CONNECTOR BETWEEN
TCM AND ATF TEMPERATURE SENSOR.
Measure resistance of harness between TCM
connector and chassis ground.

Connector & terminal

(B54) No. 11 — Chassis ground:

Does the measured value exceed the specified
value?

1 M

Ω

Go to step 5.

Repair short circuit
in harness
between TCM and
transmission con-
nector.

5

CHECK ATF TEMPERATURE SENSOR.
1) Turn ignition switch to OFF.
2) Connect connectors to transmission and

TCM.

3) Turn ignition switch to ON and start engine.
4) Warm-up the transmission until ATF tem-

perature reaches to 80

°

C (176

°

F).

NOTE:

If ambient temperature is below 0

°

C (32

°

F),

drive the vehicle until the ATF reaches its oper-
ating temperature.

5) Disconnect connector from transmission.
6) Measure resistance between transmission

connector terminals.

Connector & terminal

(T4) No. 11 — No. 12:

Is the measured value within the specified
range?

275 — 375

Ω

Go to step 6.

Replace with ATF
sensor.