TCC

📖 YOUCANIC Automotive Glossary

The TCC (Torque Converter Clutch), also called the lockup clutch or converter clutch, is a friction clutch inside the torque converter that mechanically locks the impeller (engine side) to the turbine (transmission side), eliminating the inherent fluid coupling slippage of the torque converter during cruise conditions. Without TCC lockup, the torque converter always has some degree of slip (typically 5-10%), wasting energy as heat. When the TCM commands TCC apply, the clutch plate presses against the converter housing, creating a direct 1:1 mechanical connection that improves fuel economy by 3-8% during highway cruising. Modern TCMs use PWM-controlled TCC for smooth progressive engagement.

TCC problems cause shudder or vibration during lockup engagement (worn clutch material), engine stalling when coming to a stop (TCC not releasing), surging at highway speed (TCC cycling between locked and unlocked), and poor fuel economy (TCC not locking). Common DTCs: P0740 (TCC Circuit Malfunction), P0741 (TCC Stuck Off — often caused by a worn clutch that cannot achieve lockup), P0742 (TCC Stuck On), P0743 (TCC Electrical). The YOUCANIC UCAN-II displays TCC commanded status and slip speed in live data — comparing engine RPM to transmission input RPM reveals actual converter slip and confirms whether TCC is engaging properly.