AUTOMATIC TRANSMISSION (DIAGNOSTICS)(4AT) > Diagnostic Procedure with Diagnostic Trouble Code (DTC)

DTC P0743 TORQUE CONVERTER CLUTCH CIRCUIT ELECTRICAL

DTC DETECTING CONDITION:

Output signal circuit of lock-up duty solenoid is open or shorted.

TROUBLE SYMPTOM:

No lock-up occurs. (After engine is warmed up)

WIRING DIAGRAM:

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1.CHECK DTC.

Are DTCs other than P0743 displayed?

Perform the diagnosis according to DTC.

2.CHECK HARNESS CONNECTOR BETWEEN TCM AND TRANSMISSION.

1) Turn the ignition switch to OFF.

2) Disconnect the connectors from TCM and transmission.

3) Measure the resistance of harness between TCM connector and transmission connector.

Connector & terminal

(B55) No. 6 — (B11) No. 12:

Is the resistance less than 1 Ω?

Repair the open circuit of harness between TCM and transmission connector.

3.CHECK HARNESS CONNECTOR BETWEEN TCM AND TRANSMISSION.

Measure the resistance of the harness connector between TCM connector and chassis ground.

Connector & terminal

(B55) No. 6 — Chassis ground:

Is the resistance 1 MΩ or more?

Repair the short circuit of harness between TCM and transmission connector.

4.CHECK LOCK-UP DUTY SOLENOID.

Measure the resistance between transmission connector receptacle’s terminals.

Connector & terminal

(T4) No. 12 — No. 20:

Is the resistance 2.0 — 6.0 Ω?

5.CHECK OUTPUT SIGNAL OF TCM.

1) Connect the connectors to TCM and transmission.

2) Lift up the vehicle.

3) Run the Subaru Select Monitor.

4) Start the engine.

NOTE:

If the ambient temperature is below 0°C (32°F), drive the vehicle until the ATF reaches its operating temperature.

5) Shift the select lever to “D” range, and slowly increase vehicle speed to 60 km/h (37 MPH).

6) Read the data of “Lock Up Duty Ratio” using Subaru Select Monitor.

NOTE:

The speed difference between front and rear wheels lights the ABS warning light or the VDC warning light, but this does not indicate a malfunction. If the warning light is illuminated, clear the memory of ABS or VDC after completing AT control diagnosis.

Is the measured value 95%?

6.CHECK OUTPUT SIGNAL OF TCM.

1) Return the engine speed to idle.

2) Set the select lever to “N” range.

3) Read the data of “Lock Up Duty Ratio” using Subaru Select Monitor.

NOTE:

The speed difference between front and rear wheels lights the ABS warning light or the VDC warning light, but this does not indicate a malfunction. If the warning light is illuminated, clear the memory of ABS or VDC after completing AT control diagnosis.

Is the measured value 0%?

Check the harnesses or connectors between TCM and transmission, and repair the defective part.

7.CHECK FOR POOR CONTACT.

Is there poor contact of lock-up duty solenoid circuit?

Repair the poor contact.

Replace the TCM.

8.CHECK LOCK-UP DUTY SOLENOID (IN TRANSMISSION).

1) Disconnect the transmission connector.

2) Drain the automatic transmission fluid.

CAUTION:

Do not drain ATF until it cools down.

3) Remove the oil pan.

4) Disconnect the connector from the control valve body.

5) Measure the resistance between lock-up duty solenoid and transmission ground.

Connector & terminal

(AT2) No. 6 — Transmission ground:

Is the resistance 2.0 — 6.0 Ω?

Replace the control valve body.

9.CHECK HARNESS CONNECTOR BETWEEN LOCK-UP DUTY SOLENOID AND TRANSMISSION.

Measure the resistance of harness between lock-up duty solenoid and transmission connector.

Connector & terminal

(T4) No. 12 — (AT2) No. 6:

Is the resistance less than 1 Ω?

Repair the open circuit of harness between TCM and transmission connector.

10.CHECK HARNESS CONNECTOR BETWEEN LOCK-UP DUTY SOLENOID AND TRANSMISSION.

Measure the resistance of harness between transmission connector and transmission ground.

Connector & terminal

(T4) No. 12 — Transmission ground:

Is the resistance 1 MΩ or more?

Check the harnesses or connectors between lock-up duty solenoid and transmission, and repair the defective part.

Repair the short circuit of harness between lock-up duty solenoid and transmission connector.