What does it mean?
OBD II fault code is defined as “Clutch Actuator – Circuit Low”, and is set when either the PCM (Powertrain Control Module), or TCM Transmission Control Module) detects a low voltage in the clutch actuator’s control circuit. The TCM interprets the actuator output voltage as it engages and disengages the clutch, along with that of the clutch stroke/movement sensor.
Much like fully automatic vehicles, the TCM on a SAT (Semi-automatic) vehicle uses information from a variety of sensors, such as the throttle position, engine speed, engine load, and others to calculate the correct moment when to initiate a gear change.
Gear changes are accomplished by a command from the TCM to energize the clutch actuator to release the clutch; after which various actuators inside the transmission disengage the current gear, and depending on current operating conditions, engage the next higher or lower gear ratio. All of this happens much faster than a human driver could change gears, and in most applications, gear changes are as smooth and seamless as on any fully automatic transmission.
Some types of actuators involve solenoid-type mechanisms to operate a clutch master cylinder in which power is transferred by brake fluid, such as in some Toyota models, while still other designs use electronic sensors, pneumatic and or hydraulic actuators, or a combination of sensors and different types of actuators that are controlled by microprocessors.
Regardless of the design though, the purpose of all clutch actuating systems is to improve the driving experience by removing the need for manual clutch operation by the driver. Computer-controlled clutch actuating systems work particularly well in dual clutch systems where one clutch controls gear changes of even-numbered gear ratios, and a second clutch that controls gear changes of odd-numbered ratios. The image below shows one example of a clutch actuator.
This particular unit is from Smart car, and uses an electric motor to rotate a crank-type mechanism to activate the clutch. Note that this is only one example of a clutch actuator; there are many other, different designs in use today.