Not enough water pressure to move upper arms or clean dishes

possible bad o ring to arm or weak pump

It could be a motor or a pump issue. The dishwasher has a motor that attached to a pump which forces the water up into the sprayer arms and during the drain cycle, it pushes the water out of the dishwasher.
The motor (and pump) located beneath the dishwasher.
Check if motor spins. In case it spins, the problem is with the pump ,in case it doesn't spin it could be a motor problem or a motor and pump problem.

First of all: filter plate clean? Clean any locked hole.
1) Can you remove the upper spray-arm and verify if holes inside are locked by any residus. Clean the holes , and check if pure water come out when you fill the center hole with some water.
2) Switch on the dishwasher , coldest wash cycle dish-washer empty and without the upper spraying arm. Once you hear water streaming in, open the door and look if a little water fountain comes out from the center hole where the upper spraying arm was fixed. If not, this canalisation is blocked and should be cleaned. Try to continue the wash cycle, often the water pressure will clean itself this canal. Check also lower spray arm: it should be rotating a while and ejecting water thru its holes. If not, verify this canalisation as well.

3) Put the spraying arm again on its place, verify also the sealing else water pressure is going down and spraying will not turn and spray water.

4) Again, continu a wash cycle, open the door and look; upper arm should be rotating and some rays trown out.

Hopefully, this helps .

If not, pump pressure may be low; have a repair verify, can be that only brushes in the motor must be replaced, can be the pump worn out and to be replaced at all.

Check that the arms spin freely when spun by hand, then check the outlet jets at the trailing end of the arms are not blocked with food particles and other solid matter. This often happens and the arm is unable to turn because the water jet that is supposed to drive the arm does not have the force to rotate it with the result is that the upper dishes do not get enough water and chemicals. .

How about the water inlet electrovalves, are they sticking maybe? Is there good pressure to the water inlet electrovalves from the house plumbing?

ok so If your dishwasher has worked fine in the past but, suddenly, your dishes aren't clean after the dishwasher completes all cycles:
1) Check your water heater's temperature dial to be sure it hasn't been changed recently.
2) Be sure dishes haven't prevented the detergent dispenser from opening properly during the wash cycles or kept the spray arms from turning, the lower arm from rising, or the spray from reaching the upper rack's dishes.
3) During the wash cycle, listen to the spray arm spinning inside. If it seems to be spinning poorly, clean out the spray holes in the spray arm(s) with a stiff piece of wire; wait for the machine to cool, and then remove the spray arm(s) by unscrewing the hub cap and lifting the arm(s) off Regards Gizokieth

I had the same problem and fixed it by disassembling the lower spray arm and return filter, and cleaning all the junk out.
Most dishwashers have 'risers' that bring the water up to the top sprayer or arm located under the top rack. If the recirculating pump is plugged even a little there won't be enough volume or pressure to get the water up there.
Test this by putting a dry muffin pan in the top rack, flat, and running the dishwasher for a bit. If there is no water on the top (or the bottom) either the top sprayer or the sprayer arm underneath the top rack is not getting enough volume.
To fix this you need to clean out the screen and filter, where the water returns to be recirculated. If you don't have any confidence to remove the parts and clean it out yourself, get an appliance repair person to do the job.

I removed the lower spray arm, and then the filter. I found that there was a lot of buildup under the filter area. I scraped the buildup off. I found that it was restricting the input of water flow to the pump

On the LG LDF xxxx dishwasher family, the Vario feature uses a motor/check valve to switch between "full power" cleaning from _either_ the lower or the upper spray arms, never at the same time. So, not seeing the upper arm spin during the lower arm spinning is standard operating procedure.

But back to your problem. Step one would be to remove the filter assembly again and make certain that there is nothing (debris, broken glass) blocking the white areas where the check valve rotates to switch between upper/lower spray arms. A blockage there ~could~ cause impotent spraying/cleaning.

If there is no blockage and the impeller remains in good shape, suspect a failing wash pump motor. Try to isolate the noise to that motor.

Watch for error codes on the display and report back what you find, OK?

Good Luck!

You could try running it with the upper arm removed, just so you could be sure that the pressure is not getting to that point - unless you are absolutely sure the upper arm holes/channels are all clear then descale it overnight with some vinegar - just might clear something. if there is obviously only a little flow of water then perhaps you could try getting vinegar into the supply pipe using a basting bulb/syringe or similar - again leave overnight and you may get lucky. The next thing would be to take the machine apart so you could follow this hose through to the pump - undo it from the pump and blow through it or see if you can get a piece of wire in it from the pump end. try vinegar again. check the pump outlet for blockage. Hope this helps :)

Yes I had the same problem and just fixed it for $7.00. Did not even had to take anything apart. This is what you will have to do. If this dosen't work then try what these experts are suggesting. Please follow these steps for optimal results. #1 Break off a plastic Tea spoon. #2 Put it in place of a LATCH to by pass so you can watch the operation of the dishwasher.(put down some towels for water spill) #3 start the dishwasher on normal cycle. #4 Pour in Gallon of White Vinegar($2.00) while the Dishwasher is being filled. #5 Let it run through its cycle. After the cycle is complete water will drain out and then actual cleaning cycle will start. Then #6 while the dishwasher is being filled again pour in 48 OZ or bigger bottle of CLR (Calciam Lime Rust) it is available at Meijer, walmart, Rite Aid, Home Depot Ace Menard's etc. for $5.00. sit by the dishwasher and listen for it. if you hear water draining pull and push the water plunger so it won't drain so you don't loose your CLR down the drain. since you have the spoon in the LATCH your dishwasher will always be on so BE CAREFUL when you stick your hand in it. And after the cycle is complete enjoy your NEW DISHWASHER.
Thanks
Kashif.A