CVT (continuously variable transmission)
Definition
A CVT changes ratio continuously by running a steel push belt or chain between two pulleys whose halves are moved hydraulically to vary their effective diameters, so the engine can stay at its most efficient speed; a torque converter or wet start clutch handles take-off, and most include a planetary set for reverse. The hybrid e-CVT (Toyota, Ford) is a different design with no belt - a planetary gear blending engine and two motor-generators - and shares none of the belt CVT's wear issues. Belt CVTs are sensitive to fluid condition: the specific CVT fluid provides the friction between belt and pulleys, and degraded or wrong fluid leads to belt slip, pulley scoring and metal debris that destroys the valve body and stepper motor. Symptoms are shudder or judder on take-off, a whine that rises with speed, RPM flare or hunting, hesitation and loss of power when hot, limp mode and eventually a belt that slips completely. Overheating in traffic, towing and aggressive driving shorten life sharply; change the fluid at the specified interval with the exact specification, check the level at the stated temperature and reset the fluid deterioration counter and perform the ratio learning where required. Codes: P0730 (incorrect ratio), P0776/P0777 (pressure control solenoid), P0840-P0847 (pressure sensors), P1778 (Nissan step motor), P17F0/P17F1 (Nissan CVT judder), P0868 (fluid pressure low), P0218 (overtemperature), P0715/P0720 (speed sensors), P2765 (input speed sensor B).