Every time I drive on freeways for about 20 minutes, my 2016 MDX that is four years old shows "transmission system problem", I can still drive. After you turn off the car and turn it on again, the problem disappear. I don't drive freeways often, and the problem first occurred a year ago. I went to my dealer to check the car two weeks ago. After about four hour's inspection, they found an "A/T DTC-P2638" error, and suggested me to replace the "HYDRAULIC CONTROL UNIT" which costs about $1,800. I was laid off five months ago, and have no income now. It is too expensive for me, and I don't understand completely why this unit could cause "transmission system problem. I paid $196 inspection fee and left. Today I drove on the freeway, and the problem happened again. I pulled over my, turned off the engine, then turned it on and kept driving about 10 minutes, a new error "transmission temperature too hot" showed up. I stopped immediately for about 20 minutes, then the error disappeared. I drove for about 20 minutes, then stopped about 20 minutes until I got home. Now I know I can only drive my car in the city. Should I pay $1,800 to replace the "HYDRAULIC CONTROL UNIT"? Thank you!