Why does drain pump come on immediately when turned on?

I would start with running the diagnostic mode. I know of two that I did. I'm not sure this is universal, but try one or both of these:

Diagnostic Method 1:

• With the exception of the Cycle and Start keys, press any 3 keys one after the other within a second of each other 3 times in a row, then press start.
  • Pattern: "1-2-3, 1-2-3, 1-2-3, Start" (e.g., Sani Rinse - Heat Dry - Hi Heat Wash, Sani Rinse - Heat Dry - Hi Heat Wash, Sani Rinse - Heat Dry - Hi Heat Wash, Start)
    • This will run a short test cycle and then flash a pattern of F# E# errors.

Diagnostic Method 2 (I personally felt this diagnostic mode was better) The video may be easier to demonstrate.

• https://www.youtube.com/watch?v=qhoCqLVr...

How to read the errors:

• If you see nothing but a flashing "F-" and "E-", this can mean 2 things
  • You will see this if there are no errors
  • You will see this after any errors have been identified
  • If there are errors, it will flash an "F#" and "E#" about 3 times so you can write them down, then move to the next error or flash "F-" "E-"

Interpreting Error Codes:

• If you have your Dishwasher documents, there is a "Service Technician" document intended for use by service techs that lists all the codes and their meanings. You can also search the Internet and easily find them. However, the Service Tech document is more thorough, whereas, some webpages provide the common errors. You can also just enter the error code and find out what it is: "Whirlpool Dishwasher F8 E4"

I just recently fixed my Whirlpool Dishwasher (gold series) and replaced the circulation pump and inlet valve using these methods and it runs great. Whereas, it was filling and draining, but not washing.

Good luck!