Step 13 - Inspect Open Door Warning Light
WARNING: This page is about a different car, the 2002 Toyota Prius. However, it is still accessible from the selected car via links, so may be relevant.
Disconnect the connector from the door courtesy switch, and ground terminal 1 of the wire harness side connector and check that the warning light lights up.
If the warning light does not light up, inspect the bulb or wire harness.