The P0742 code in your 2019 Genesis G80 indicates that the torque converter clutch is stuck in the engaged position. When the TCM commands the TCC to release, it fails to disengage. This is the opposite problem of P0741—instead of not locking up, the TCC won't unlock when it should.
TCC Stuck On Problems
When the TCC won't release, the direct mechanical connection between engine and transmission remains constant. This causes problems at low speeds and during stops because the engine and transmission are locked together. Your G80 may stall, buck, or experience harsh engagement.
Common Causes
The TCC solenoid may be stuck in the apply position. Valve body issues trapping pressure in the TCC apply circuit. Warped or damaged TCC components preventing release. Hydraulic pressure problems keeping the TCC applied. Wiring issues commanding TCC on when it should be off.
Symptoms You'll Experience
Engine stalling when coming to a stop, as the locked TCC drags down the engine. Harsh, jerky engagement when accelerating from a stop. The vehicle may lurch or buck at low speeds. Vibration or shudder during TCC transitions. Check engine light with P0742 stored.
Genesis Diagnostic Procedure
Using Hyundai/Genesis GDS, monitor TCC status during various driving conditions. When commanded off, does slip appear between engine and transmission input speed? If they remain locked, the TCC isn't releasing. Test solenoid function—it should allow pressure release when de-energized. Check for stuck valves in the valve body.