Faulty torque converter clutch solenoid (open or shorted winding); Damaged, chafed or corroded wiring between the solenoid and the transmission control unit; Poor connection at the gearbox internal harness connector or control unit plug, including contamination by fluid; Low, degraded or contaminated transmission fluid affecting the solenoid or valve body; Low battery voltage or poor earth causing unstable supply to the control unit; Faulty transmission control unit or driver circuit; Valve body or internal gearbox fault, depending on the transmission design.

P0743

Torque Converter Clutch Circuit Electrical.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
7: AreaTransmission
43: FaultThe specific fault in that area

What it means

P0743 is the generic code for an electrical fault in the torque converter clutch (TCC) circuit. The transmission control unit commands the TCC solenoid on and off, and it has detected an open circuit, short circuit or voltage that does not match what it expects. The exact circuit layout and test values depend on the vehicle and gearbox.

Symptoms

Malfunction indicator lamp on, possibly with a gearbox warning lamp
Transmission may stay in limp mode or avoid top gear
Torque converter does not lock up, so revs sit higher at cruising speed
Higher fuel consumption on motorways
Shudder, hesitation or stalling when slowing to a stop
Harsh or unusual shifts in some cases

Possible causes

Faulty torque converter clutch solenoid (open or shorted winding)likely
Damaged, chafed or corroded wiring between the solenoid and the transmission control unitlikely
Poor connection at the gearbox internal harness connector or control unit plug, including contamination by fluidlikely
Low, degraded or contaminated transmission fluid affecting the solenoid or valve bodypossible
Low battery voltage or poor earth causing unstable supply to the control unitpossible
Faulty transmission control unit or driver circuitrare
Valve body or internal gearbox fault, depending on the transmission designrare

How to diagnose

Read all stored and pending codes and note the freeze frame data to see the conditions when the fault set
Check for related codes such as battery voltage, speed sensor or other solenoid faults and deal with those first if present
Check transmission fluid level and condition using the manufacturer's procedure for the gearbox fitted
Inspect the wiring and connectors from the gearbox to the control unit for chafing, heat damage, corrosion, or fluid ingress
Check battery condition, charging voltage and the relevant earth connections
Measure the TCC solenoid resistance at the connector and compare it with the specification for that model
Test the circuit for continuity, short to earth and short to supply, then check for command signal from the control unit
Use a scan tool's live data and active test, if supported, to see whether the solenoid responds to commands

How to fix

Repair or replace damaged wiring and terminals in the TCC circuit
Clean, reseat or replace the affected connector, and replace the internal harness if fluid has wicked into it
Replace the TCC solenoid if its resistance or operation is out of specification
Correct the fluid level, or service the transmission fluid and filter where the manufacturer allows it
Repair battery, charging or earth faults
Repair or replace the transmission control unit only after the wiring and solenoid have been proven good, and check whether a software update applies to that model

Can I keep driving?

Medium severity

The car can usually be driven short distances, but expect poor economy and possible limp mode. Get it checked soon, as continued driving with no lock-up, or with a shudder, can overheat the fluid and cause further transmission wear.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.