the rear passenger door will lock using the key fob but will not unlock, all other functions are ok, i have a 2003 xj6 v6 se

 

Not sure how or if the child lock figures into this but give it a try located on the door seal/edge.

 

Possibly sounds like the mechanism brushes are failing....the pulling action is easier than the pushing. It could be gunked also, simply spraying the cable (clean any noticeable clutter) and latching mechanism with some dry lube silicone spray (yeah, sounds like an oxymoron) may cure the issue also. Function the latch, put a screw driver in it to engage it, spray again, retract,...spray, ...engage, ....spray ...until it operates smoothly. If it doesn't after that, back to the mechanism failing.