What P0743 means
The torque converter clutch (lock-up) connects pump and turbine mechanically; a solenoid – on/off, pulse-width modulated or proportional – moves a control valve in the valve body.
How the engine computer detects it
Slip is engine speed minus turbine speed. Manufacturers do not use P0740–P0744 uniformly: Ford uses P0740 for open, P0742 for short to ground and P0744 for short to power, and reports stuck on as P2758. P0743 is the collective electrical code for the converter clutch solenoid circuit – open, short to ground or to positive – detected by terminal voltage, driver feedback or current. Subaru flags it after 0.14 s and lights the MIL after two trips, Saab's 9-3 of 2003 above 1356 mA for 500 ms, Allison after 1.5 s; older Ford transmissions also use it. The clutch is switched off; Saab's Aisin boxes go into limp mode, Subaru does not.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- Check engine light or transmission warning
- No lock-up: engine speed about 100–300 rpm higher when cruising
- Limp mode on some makes (Saab/Aisin)
Common causes
- Transmission harness or pass-through connector (corrosion, chafing, oil in connector) Most likely
- Solenoid coil open or shorted Most likely
- Internal harness or mechatronic unit Possible
- Driver stage in the transmission or engine module Less likely
How to diagnose P0743
- Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
- Inspect the parts involved: torque converter clutch solenoid, torque converter, transmission valve body, transmission control module.
- Work through the causes above from most to least likely, cheapest checks first.
- Clear the code and drive a full drive cycle to confirm the repair held.
Reading the code
- P
- Powertrain
- 0
- Generic (SAE) code
- 7
- Transmission
- 43
- Specific fault
Questions drivers ask
Can I drive with code P0743?
If the car shifts normally, drive gently to a shop. If it's stuck in one gear, slips, shifts harshly or won't move out of Park, don't drive it: have it towed.
Will my car pass an emissions inspection with P0743?
Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.
Will P0743 clear by itself?
The light can go off after several drive cycles without the fault, but the code returns if the cause is still there. After a repair, the readiness monitors need a full drive cycle before an inspection.
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.