panei

It is intransitive, and that matters. A thing paneas. You cannot panei a thing. Mi paneis la aŭton is not Esperanto; if you broke it deliberately, that is mi paneigis la aŭton with -ig-, or more naturally mi difektis or mi rompis it. The transitivity article is worth a look if this distinction is still costing you sentences, because Esperanto enforces it much more strictly than English does.

What it covers. A vehicle that stops, a machine that quits, a lift stuck between floors, a power cut, a computer that crashes, a process that seizes up. The noun is paneo, a breakdown. Near neighbours: averio is damage sustained, especially at sea; difektiĝi is to become faulty; rompi is to break in the physical, pieces-on-the-floor sense. Panei is specifically about ceasing to function, and it says nothing about whether anything is actually broken.

Three words one letter apart, and none of them related.Pano is bread, from Latin panis. Panero is a breadcrumb, which is pano plus -er-, the fragment suffix. Paneo is a breakdown, from French panne. So panero and paneo differ by one letter and by an entire etymology, and a panerujo is a breadcrumb tin while a paneo is your morning ruined. Read the endings carefully.