DTC P0743 Torque Converter Clutch Circuit Electrical

WARNING: This page is about a different variant/trim than selected.

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:

Fig 1: Wiring Diagram - Torque Converter Clutch Circuit (Electrical)

Courtesy of SUBARU OF AMERICA, INC.

DTC P0743 DIAGNOSTIC PROCEDURE

Step	CHECK	Yes	No
1 CHECK DTC.	Do multiple DTC appear in the on-board diagnostics test mode?	Go to another DTC.	Go to step 2 .
2 CHECK HARNESS CONNECTOR BETWEEN TCM AND TRANSMISSION. Turn the ignition switch to OFF. Disconnect the connector from TCM and transmission. Measure the resistance of harness between TCM and transmission connector. Connector & terminal (B55) No. 5 - (B11) No. 12:	Is the resistance less than 1 Ω?	Go to step 3 .	Repair the open circuit in harness between TCM and transmission connector.
3 CHECK HARNESS CONNECTOR BETWEEN TCM AND TRANSMISSION. Measure the resistance of harness connector between TCM and chassis ground. Connector & terminal (B55) No. 5 - Chassis ground:	Is the resistance more than 1 MΩ?	Go to step 4 .	Repair the short circuit in 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?	Go to step 5 .	Go to step 8 .
5 CHECK OUTPUT SIGNAL EMITTED FROM TCM USING SUBARU SELECT MONITOR. Connect the connectors to TCM and transmission. Lift-up the vehicle and support with rigid racks. NOTE: Raise all wheels off floor. Connect the Subaru Select Monitor to data link connector. Start the engine, and turn the Subaru Select Monitor switch to ON. Start the engine and warm-up the engine until the ATF temperature is above 80°C (176°F). NOTE: If the ambient temperature is below 0°C (32°F), drive the vehicle until the ATF reaches its operating temperature. Read the data of "Lock-Up duty Ratio" using Subaru Select Monitor. Lock-up duty solenoid is indicated in "%". Shift the select lever to "D", and slowly increase vehicle speed to 60 km/h (37 MPH). NOTE: The speed difference between front and rear wheels may light the ABS warning light, but this indicates no malfunction. When AT control diagnosis is finished, perform the ABS memory clearance procedure of on-board diagnostics system. < Ref. to CLEAR MEMORY MODE . >	Is the value 95%?	Go to step 6.	Go to step 7.
6 CHECK OUTPUT SIGNAL EMITTED FROM TCM USING SUBARU SELECT MONITOR. Return the engine to idling speed, shift the select lever to "N" range and read data. NOTE: The speed difference between front and rear wheels may light the ABS warning light, but this indicates no malfunction. When AT control diagnosis is finished, perform the ABS memory clearance procedure of on-board diagnostics system. < Ref. to CLEAR MEMORY MODE . >	Is the value 5%?	Even if the SPORT indicator light is blinking, the circuit has returned to normal condition at this time. A temporary poor contact of connector or harness may be the cause. Repair the harness or connector in TCM and transmission.	Go to step 7.
7 CHECK POOR CONTACT.	Is there poor contact in lock-up duty solenoid circuit?	Repair the poor contact.	Replace the TCM. < Ref. to TRANSMISSION CONTROL MODULE (TCM) . >
8 CHECK LOCK-UP DUTY SOLENOID (IN TRANSMISSION). Disconnect the transmission connector. Drain the ATF. CAUTION: Do not drain the ATF until it cools down. Remove the oil pan, and disconnect the connector from control valve body. Measure the resistance between lock-up duty solenoid and transmission ground. Connector & terminal (AT3) No. 4 - Transmission ground:	Is the resistance 2.0 - 6.0 Ω?	Go to step 9 .	Replace the control valve body. < Ref. to 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 - (AT3) No. 4:	Is the resistance less than 1 Ω?	Go to step 10 .	Repair the open circuit in 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 more than 1 MΩ?	Even if the SPORT indicator light is blinking, the circuit has returned to normal condition at this time. A temporary poor contact of connector or harness may be the cause. Repair the harness or connector in lock-up duty solenoid and transmission.	Repair the short circuit in harness between lock-up duty solenoid and transmission connector.