Washer stuck on 2nd rinse

Why is my washing machine stuck on the 2nd (optional) rinse? The initial wash and rinse and spin all work fine and timer advances correctly however if the 2nd rinse option is selected, it gets stuck and won’t advance once it reaches the 2nd rinse. The timer doesn’t move and the water keeps flowing in. I have a Kenmore top loader 80 series. Thanks for any help!