A gearbox assembly includes a housing, an output shaft, a wheel gear, an input shaft, a torsion bar, an electric motor, a worm gear and a key lock. The wheel gear may be fixed to the output shaft for engagement with a wheel gear. The torsion bar may connect the input shaft to the output shaft. The worm gear may be rotationally fixed to the rotor and engages the wheel gear to transfer torque from the motor to the output shaft. The key lock may include an adapter, an annular outer part, a web, and a locking collar. The key lock may be fixed to the housing and is movable between an extended position in which a part of the key lock engages the locking collar and a retracted position in which the part is held clear of the locking collar.