We never noticed about the headrests NOT moving up/down although we can hear the motor running when we press the switch. This is how we fixed ours, they do move up/down for many years now.
Headrest Fix Procedure: This is the way I fixed mine, use it at your own risks since it requires modification to original equipments.
* Use power seat button to move the seats forward as far as we could.
* Fold the back of the seat forward as far as we could.
* We need to remove the back panel, use a letter opener or a screw driver carefully to pry the seams off the back panel.
Use the fingers to pull the rubber seal off the back panel slowly and carefully until it clears the groove.
We need to remove the 2 philips screws 1 on each side of the seat to remove the back panel.
When the screws are out, pull the back panel down and out slowly and carefully.
The motor is on the left side of the seat
There are 2 8mm bolts need to be removed to remove the motor.
When the bolts are out, we can take out the motor from the bracket, just pull the cable straight out, watch out not to get the inner cable dirty. Don’t forget which side is which.
The problem when the motor turns but the headrest doesn’t move up or down is because of the inner cable doesn’t make contact with the headrest slot, it’s shorter than the cable sleeve for some reason. We need to shorten the cable sleeve (black plastic shield part) so the inner cable will extrude more than before.
We cut 1/3 inch off the original cable, it’s better to cut it little by little than cut all at once toooo much. And where to cut is very important. Make sure we have enough room for the rubber tube and tie-wrap to tighten it.
We use 5/16 fuel hose to clamp the 2 separate plastic sleeve (shield) together using tie-wrap or fuel hose metal clamps. We found the tie-wraps are efficient.
Since we used the tie-wrap, we make sure all grease was wiped clean before the fuel hose slide on and pulled real tight with the joint is in the middle of the fuel hose. Grease may cause the 2 cable slide apart and we won’t have the inner cable connection again. MAKE SURE THE 2 SLEEVE JOINT IN THE MIDDLE.
Put back the motor to the bracket and test it out before putting back the back panel and everything else. It should work very nicely, up/down. If it doesn’t, we cut it too little or the joint is separate (have big gap under the fuel hose). Push the 2 shields (sleeve) together and re-clamp.
I’m sure there are many ways to do this, but this is the way I did mine. It’s important not the cut off too much of the sleeve and tie-wrap the fuel hose tightly not to fall off later.
Cheers and good luck,