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Home >> Subaru >> 2006 >> Legacy GT spec.B >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 16 (Automatic Transmission (Diagnostics) 4AT) >> Diagnostic Procedure with Diagnostic Trouble Code (DTC) >> DTC P0743 Torque Converter Clutch Circuit Electrical

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: Lock-Up Duty Solenoid - Wiring Diagram
G05019781
RESISTANCE CHART

Step Check Yes No
1 CHECK DTC.  Do multiple DTCs appear in the on-board diagnostics test mode? Go to other DTC. Go to step 2. 
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 the harness between TCM connector 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 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. 5 - Chassis ground: 		 Is the resistance more than 1 MΩ? Go to step 4.  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 between 2.0 - 6.0 Ω? Go to step 5.  Go to step 8. 
5 CHECK OUTPUT SIGNAL FROM TCM USING SUBARU SELECT MONITOR. 
  1. Connect the connectors to TCM and transmission.
  2. Lift up the vehicle and support with rigid racks.
    NOTE: Raise all wheels off the floor.
  3. Connect the Subaru Select Monitor to the data link connector.
  4. Start the engine, and turn the Subaru Select Monitor power switch ON.
  5. Start the engine and warm-up the engine until the ATF temperature exceeds 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.
  6. Read the data of "Lock Up Duty Ratio" using Subaru Select Monitor.
    • Lock up duty solenoid is indicated in "%."
  7. 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 does not indicate a 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 measured value 95%? Go to step 6.  Go to step 7. 
6 CHECK OUTPUT SIGNAL FROM TCM USING SUBARU SELECT MONITOR. 
Return the engine to idling speed, shift the select lever to "N" range and read the data.
NOTE: The speed difference between front and rear wheels may light the ABS warning light, but this does not indicate a 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 measured value 5%? Even if the SPORT indicator light is blinking, the circuit is in 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). 
  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, and disconnect the connector from control valve body.
  4. Measure the resistance between lock-up duty solenoid and transmission ground.

    Connector & terminal 

    (AT12) No. 4 - Transmission ground: 

 Is the resistance between 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 - (AT12) No. 4: 		 Is the resistance less than 1 Ω? Go to step 10.  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 more than 1 MΩ? Even if the SPORT indicator light is blinking, the circuit is in 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 of harness between lock-up duty solenoid and transmission connector.
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