2003 Mini Cooper Base, Automatic CVTFACTORY OEM SERVICE PROCEDURE

ECVT Principles

Unlike conventional planetary automatic transmissions that provide a limited number of gear ratios, usually three, four or five, the ECVT, as its name suggests, continuously varies the gear ratio.

A low gear (low ratio) makes it easier to pull away from a rest position, the drive pulley being relatively small, while the driven pulley is large by comparison. The drive belt is used to transmit power and torque.

The ECVT uses a primary pulley and a secondary pulley. Both pulleys have one fixed half and one mobile half, controlled by hydraulic pressure. The position of the drive belt on the pulleys will determine the ratio. If the mobile half of the pulley is close to its opposite half then the drive belt is forced to travel around the outer circumference. When the pulley is open wide then this circumference is reduced. The primary and secondary pulley mobile halves are diagonally opposed so when the drive belt diameter is reduced on the primary pulley, it increases on the secondary pulley.

To pull away, a low ratio is required. To provide this, the primary pulley is open, allowing the drive belt to sit down into the pulley and forcing it to run around the outer part of the closed secondary pulley.

Fig 1: ECVT Pulleys In Low Position
G04724792Courtesy of BMW OF NORTH AMERICA, INC.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • β€’ You smell fuel, burning insulation, or see smoke.
  • β€’ Brakes feel soft, pull hard to one side, or make grinding noises.
  • β€’ The engine overheats, stalls repeatedly, or misfires under load.
  • β€’ You are missing required tools, torque specs, or safe lifting equipment.
  • β€’ You are not confident in the next step or safety outcome.

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