Corolla automatic transmission shifting issue

Sounds familiar. I've got a Corolla too, though I never saw an indicator light. But the shifting was wonky, like the gears were coated in molasses. Have you checked for undervoltage?

Undervoltage? How would that affect the transmission? I've not looked at that yet...

Yeah, apparently low voltage can mess with the electronic controls for the transmission. It's like trying to run a computer on a nearly dead battery – things get glitchy. Best get it checked professionally; a transmission flush might be needed.

Thanks for the tip! You were right. The workshop found an undervoltage issue. They sorted that and did a transmission oil change, and it's running smoothly again. Cost me 240€, but worth it.