Clause coordination joins clauses that stand at the same level. Neither clause fills a place inside the other. A word such as and, but, or or marks the connection between them.
The engine stalled and the car stopped are complete clauses. The coordinator joins them at the same level.
the test
Make two sentences
The engine stalled. The car stopped.
For this full-clause example, each coordinate can also be written as a sentence. That supports their equal status here; it does not define every coordination, since coordinated clauses can share or omit recoverable material. By contrast, because the belt broke gives a reason inside a larger relationship.
Does a comma change the structure?
No comma: two short coordinated clauses.
The comma helps a reader see the boundary. The two clause frames and their coordinator establish the coordination.
Equal status does not mean interchangeable order.
Reversing coordinated clauses can change event order, cause, or emphasis. Their equality comes from the fact that neither is a dependent inside the other, not from a promise that they can swap places.
Ten sentences from this lesson, one decision at a time.