I have model number WFW9400SW03 I get error code F 71 then at times it switches to F70

Both of those error codes have to do with bad communication between the interface and main control boards. You need to replace the boards. The boards you need to replace are linked below.

User interface boards : https://prismparts.com/products/washer-interface-control-boards-part-number-rp0518354paz85

Main control board: https://prismparts.com/products/washer-electronic-control-board-part-number-rp5328106paz54

Once those are replaced the washer will be fine. They are both located in the top of the washer. The video linked below will give you some idea of how to access and replace the user interface boards. 

https://www.youtube.com/watch?v=2_wrqiVWOqs&ab_channel=PCApplianceRepairIsNowAppliancePartsExperts

The video linked below here will show you how to replace the main control board.

https://www.youtube.com/watch?v=ek9ll3mPryE&t=72s&ab_channel=RepairClinic.com

Hope this helps.