Thanks CJ for sending me the instruction on how to access the headrest motor. A found the problem which was'nt really critical. The gear on the rail overshoot it in the downward direction (out of the rail gear). The repair process was simple, I disassemble the gear housing and reposition the gear in the rail. The only hard part was the removal of the backrest cover aside from the two screws that hold the buttom part. You have to fry out both the side seats cover with the flat tip screw driver.