P0743

Schematic:

Circuit Description with 4L30-E Automatic Transmission
The Torque Converter Clutch (TCC) solenoid is located in the transmission adapter case. The solenoid valve controls the engagement and disengagement of the torque converter clutch in 3rd and 4th gears. The TCC operation is dependent on transmission fluid temperature, selected shift program and vehicle speed. The TCM controls the TCC solenoid and the solenoid controls transmission fluid flow to the TCC.

The TCC solenoid is supplied power via the Transmission Power Relay (internal to the TCM). The TCM controls the solenoid by grounding the control circuit via an internal solid state device called a driver. The driver has a fault line which the TCM monitors. When the TCM commands the TCC on, the voltage of the control circuit should be low (near 0 volts). When the TCM commands the TCC off, the voltage potential of the circuit will be high (near the system voltage). When the TCM detects a continuous open, short to ground, or a short to power in the TCC solenoid circuit or in the TCC solenoid valve, then DTC P0743 sets. DTC P0743 is a type B DTC.

CONDITIONS FOR RUNNING THE DTC
^ TCC is commanded OFF.
^ The TCM High Side Driver is closed.

CONDITIONS FOR SETTING THE DTC
^ A short to ground:
TCM detects less than 2.45 volts for 0.18 seconds on the control circuit.
^ Open circuit:
TCM detects 2.45-3.53 volts for 0.18 seconds on the control circuit.
^ Short to battery:
TCM detects more than 4.02 volts for 0.18 seconds on the control circuit.

ACTION TAKEN WHEN THE DTC SETS
^ The TCM flashes the sport mode lamp and sends a MIL request to the ECM on the second consecutive drive trip that the diagnostic runs and fails. The ECM then illuminates the MIL.
^ The ECM records the operating conditions in the Freeze Frame at the time of the MIL request from the TCM.
^ The transmission operates in the default mode (maximum line pressure, command 4th gear, inhibit TCC, freeze shift adapts).

CONDITIONS FOR CLEARING THE MIL/DTC
^ The ECM turns off the MIL after three consecutive drive trips during which the TCM sends no MIL request.
^ A History DTC clears after forty consecutive warm-up cycles, if no failures are present by this diagnostic or any other emission related diagnostic.
^ The scan tool clears the MIL/DTC.
^ The TCM cancels the DTC default mode actions when the ignition switch is Off long enough in order to power down the TCM.

DIAGNOSTIC AIDS
Use the J 35616-A connector test adapter kit for any test that requires probing the TCM harness connector or a component harness connector. Using this kit will prevent damage to the harness connector terminals.

Check for the following conditions:
^ Poor connections at the TCM or at the component. Inspect the harness connectors for any backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
Refer to General Electrical Diagnosis Procedures in Diagrams for proper procedure.
^ Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the scan tool while moving any related connectors and any wiring harnesses. A change in the display may help to locate the fault.

TEST DESCRIPTION

Steps 1 - 3:

Steps 4 - 15:

The numbers below refer to the step numbers on the diagnostic table.
2. Listen for an audible click when the solenoid operates. Ground the circuit repeatedly if necessary.
7. If the TCC solenoid valve checks out OK and no condition is found with the connections at the TCM, check the wiring and connections closely. If no condition is found, the TCM may be the cause of the condition.