Error code er ff.how do i fix this?

The error code appears when there is an abnormality of BLDC FAN Motor for Freezer. It circulates cold air from the freezer to the fridge to allow cooling. Check the motor wiring harness for poor connections. If the motor is not working at all, you need to replace it.
To remove the fan and motor assembly:

1. Remove the freezer shelf. (If your refrigerator has an
   icemaker, remove the icemaker first).
2. Remove the plastic guide for slides on left side by
   unscrewing phillips head screws.
3. Remove the grille by removing one screw and pulling the
   grille forward.
4. Remove the Fan Motor assembly by loosening 2 screws
   and disassembling the shroud.
5. Pull out the fan and separate the Fan Motor and Bracket.
6. Replace fan motor assembly in reverse order.
   

We got the same problem. This model is a total POS. We had to empty the fridge and let it thaw. LG told us the freezer fan froze up. Sure enough after 24 hours, there was a puddle of water under the fridge. Now that works, but the ice maker broke. Not what you'd expect from a $2500 fridge. There are TONS of complaints about this out there.