Embrayage de convertisseur qui patine

The lock-up clutch inside the torque converter transmitting less than it should, so engine speed and transmission input speed no longer agree when the clutch is applied. This entry is about the slip being observed in the ratio, which is why it sits on gear ratio and engine speed codes rather than on the clutch's own circuit codes — the module notices the mismatch before it notices anything wrong with the clutch.

The symptom is a subtle rise in engine speed with no change in road speed, usually at light throttle in the highest gear where lock-up lives, often felt as a shudder rather than heard. It is easily read as a worn gearbox, because incorrect-ratio codes are exactly what a mechanical fault produces, and the converter is the one part of the transmission nobody can see.

Fluid condition is the first thing to establish, not the last. The lock-up clutch is a friction surface running in the fluid, and fluid that has overheated loses the friction properties the clutch depends on — which is why a deteriorated-fluid code and a slipping clutch appear together so often. A slip that begins after the fluid has cooked is a consequence, and replacing the converter without addressing why the fluid overheated leaves the new one in the same conditions.