What does it mean?
OBD II fault code P0901 is a generic code that is defined as “Clutch actuator -circuit range/performance”, and is set when the PCM (Powertrain Control Module) detects a problem in the control circuit of the clutch actuator that affects the range or performance of the clutch actuator. Note that code P0902 refers to a problem with either the clutch actuator itself, or with the clutch actuator’s control circuit.
On applications that are fitted with automated manual transmissions, which are normal manual transmissions that are fitted with computer-controlled shift mechanisms, the clutch is also controlled by the PCM by means of an actuator that can be electrically (most commonly) or hydraulically operated.
When the PCM determines that a shift point had been reached, it actuates the clutch to decouple the transmission from the engine, after which actuators deselect the current gear, and depending on the operating conditions, selects the next higher or lower gear. When the PCM receives confirmation from various position sensors that the next gear had been selected successfully, it again activates the clutch actuator to re-engage the clutch, which “reconnects” the engine to the transmission.
Note that the position of the clutch actuator is continually being monitored by the PCM. Thus, when the PCM detects a fault condition, electrical failure, or malfunction in the actuator control circuit that prevents the clutch actuator from fully disengaging/re-engaging the clutch, or if it receives a signal from the clutch actuator position sensor that does not agree with the desired or expected position of the clutch actuator it will set code P0901, and may also illuminate a warning light.
The image below shows a typical clutch actuator but note that the appearance, and operating principles of clutch actuators vary between manufacturers. Refer to the manual for the application for details on the location and operating principles of the clutch actuator on the affected application.