Why does a dual-clutch transmission lack power in reverse or roll back?
2 Answers
The phenomenon of a dual-clutch transmission lacking power in reverse or rolling back mainly stems from its structure. Some manufacturers call it DSG, while others refer to it as DCT, but they all rely on the working structure of two clutches. This clutch is similar to the one we used when learning to drive, except now it is controlled by a computer, which solves the difficulty of operation but cannot address the issue of semi-engagement. In theory, a dual-clutch transmission does not have the concept of semi-engagement; it only has the notions of engagement and disengagement. Therefore, when the program determines that the clutch is disengaged, the reverse gear lacks power and the vehicle rolls back. When we release the throttle, the program likely causes the clutch to disengage, resulting in no power and the vehicle rolling back due to gravity. Of course, some transmission programs are slightly better. For example, after releasing the throttle, there is still a 1-2 second engagement period. During this time, even if the throttle is released, the engine's torque can still keep the vehicle stationary or moving slowly, preventing immediate rolling back.
I've experienced this situation before when driving a dual-clutch car, which is actually related to the working principle of the clutch. During reverse gear engagement, only one clutch plate is engaged in a dual-clutch transmission, resulting in inherently weaker torque output. If the car is parked on a slope, the system detects the risk of rolling and automatically reduces clutch pressure to prevent overheating, leading to less smooth power delivery. Once when reversing on an underground garage ramp, I distinctly felt intermittent power delivery, only to learn later it was due to the combined effect of hill start assist and clutch protection. Additionally, minor leaks in the hydraulic control system, excessively high transmission fluid temperature, or severely worn clutch plates can exacerbate this situation. For slope reversing, I recommend applying more throttle to activate hill start assist. If this occurs frequently, it's best to read the fault codes for diagnosis.
