Same issue
Hello,
I'm having the exact same issue. The key fob, drivers electronic unlock switch, and passenger unlock switch all only unlock the drivers door. All doors do lock electronically. Issue was intermittent at first, however eventually became permanent.
After reading this post and about 20 other threads with similar no results, I decided to buy the service manual and do some reading. (caveat to this post, the service manual I bought was only valid through 2013 Sorento. I'm assuming not much has changed however. I'm waiting for an exchange from the site I bought the manual from to confirm).
I haven't fixed it yet, however will work on it here soon and have a pretty good guess as to what the problem is. The actual unlock logic is controlled by a microcontroller and has a dizzying amount of different logic states, however the fact that the indoor unlock buttons still unlock the drivers door seems to indicate that is getting out of the logic states and at least trying to unlock the doors.
On the European models, all four doors are tied together to the same two relays, a lock and unlock. On North American models there is there relays, a door lock relay, a driver door unlock relay, and a door unlock relay. This is loosely referred to as two step or two turn unlock system depending on which chapter you are reading. The door lock is shared between all doors and completes the circuit with either the driver door unlock relay, or the rest of the doors unlock relay. All are connected to VCC by default so there is no voltage difference across the motors. I'm guessing the non-drivers door unlock relay is getting stuck in an off state, so it can still source current for locking but won't sink current for unlocking.
Where to find the relays was not explained very well at all. The DR LOCK fuse for the relays was in tact (not surprising since the driver door unlocks) and the description says Door Lock/Unlock Relay, ICM Relay Box (two turn unlock relay)… etc. so my first thought was ICM relay box. However, no where in the description for the ICM does it mention anything about door relays. As best as I can tell (their manual is not very clear on this), they appear to be located on the BCM (IPM) board (ouch $$$). The IO for this lists all three relay "Outputs" indicating the relays are co-located. Unfortunately it doesn't look like this is one of the replaceable relays so naturally there is no documentation on what physical component it is.
Since I'm sure I'll be looking at $800-1000 for a dealer to replace this, and even buying the part online is ~$300+ which is a little over my risk threshold. I'm going to see if I can track down where the relay is physically on the board and what it would take to replace it. If I find a solution I'll update the forum here.
If anyone knows where a BCM assembly drawing or schematic could be found... I'd appreciate it. It is not in the service manual.