Diagnostic apparatus and diagnostic method for belt squeezing force adjusting mechanism

A diagnostic apparatus for a belt squeezing force adjusting mechanism of a continuously variable transmission in which a belt is wound around a primary sheave that receives driving force and a secondary sheave that outputs force to a drive-line, and which continuously changes the output rotation speed by adjusting the width of the groove of the primary sheave and the secondary sheave by shift control of controlling an actual control value responding to a target control value, comprising:

• an electronic control unit, configured with executable program logic, to perform:
• determining, as a precondition, whether a target control value calculated in shift control is in a lower region than a region of the control value that can be reached when the belt squeezing force adjusting mechanism is malfunctioning;
• and
• performing, when it has been determined that the precondition is satisfied, a diagnostic on the belt squeezing force adjusting mechanism based on the relationship between the actual control value and the target control value when the control value is reducing due to the shift control,
• wherein the ECU determines that there is a malfunction in the belt squeezing force adjusting mechanism when the actual control value has difficultly coming close to the target control value during the control to reduce the control value, and
• wherein the ECU determines that the belt squeezing force adjusting mechanism is functioning normally when the actual control value is able to come close to the target control value.