I've read through the various threads in this forum and haven't seen my particular problem. I have an 05 F-150 King Ranch Super Crew. So, here goes:

I can't lock the doors with the switch (driver's or passengers). The autolock feature doesn't seem to work. The key fob will not lock the doors. I don't seem to hear the relays actuating any place. The switches & key fob will unlock the doors without a problem. Are there any easy checks to troubleshoot this problem ?? I gather it could be a relay or some central module. Any easy advice other than going to the dealer ?? I have checked fuses 22 and 28. They seem to be ok.

The door locks never seemed to get sluggish, BTW

 

Same problem here. BUMP!!!

 

try replacing 1 actuator.. may have problems locking but notunlockin

 

I'm looking at replacing my actuator too, drivers side. It unlocks and locks OK, but sometimes has a hard time going all the way up or down, struggling, but the thing does it ok by hand. I figure it's the actuator so I'm getting a new one.

 

Note this thread... have '97 that will 'unlock' all day long with the door toggle but will NOT 'lock' - no fob, so it is not in use.
This seems to 'come and go' - works for a week, stops for a day or two, starts again working, goes off for a week - as BOTH switches stop and work at the same time, don't think this is an actuator (but?) - and CANNOT find the relay for this 'door lock'? Thanks.

 

Turns out it was a couple of problems; the keyless entry was shorted and the security module was defective. It's likely that the keyless entry short killed the security module. I question as to why the keyless entry component was shorted. All I will say is that I'm thankful that I had the foresight to obtain the extended warranty, as these components failed just 5000 miles/ one month past the factory warranty.