În cazul în care stopul este defect, mașina este respinsă.

It literally means in the case in which. In natural English, it usually corresponds to if or in the event that.

In Romanian, în cazul în care is more:

• formal
• technical
• administrative/instructional

So it fits well in sentences about rules, inspections, and procedures.

Yes. You could say:

Dacă stopul este defect, mașina este respinsă.

That would mean essentially the same thing. The difference is mostly register:

• dacă = normal, everyday if
• în cazul în care = more formal, more official-sounding

The original sentence sounds like something from a vehicle inspection manual or regulation.

Yes, but not in the same way an English speaker might expect.

In Romanian, stop in a car context usually means a rear light / taillight / brake light unit. So stopul here is not the verb to stop, and it is not a road STOP sign.

So this is a good vocabulary item to learn as a somewhat specialized automotive meaning.

Because Romanian usually puts the definite article at the end of the noun.

So:

• stop = a taillight / a rear light
• stopul = the taillight / the rear light

That -ul is the masculine/neuter singular definite article.

This is very different from English, where the is a separate word.

Because defect agrees with stopul, which is treated here as a masculine singular noun.

So:

• stopul este defect = the light is defective

Romanian adjectives change form to match the noun.

Compare:

• stopul este defect → masculine singular
• mașina este defectă → feminine singular

So the form depends on the noun being described.

Here it is an adjective meaning defective, faulty, or broken.

So:

• este defect = is defective / is faulty

Romanian often uses a fi + adjective in exactly this way.

It is a passive construction.

• este = is
• respinsă = rejected / failed (past participle used in the passive)

So:

• mașina este respinsă = the car is rejected / the car fails

This kind of passive is very common in official or technical Romanian.

Because respinsă agrees with mașina, and mașina is feminine singular.

So:

• mașina este respinsă = feminine singular
• automobilul este respins = masculine singular

Again, Romanian participles/adjectives usually agree with the noun they describe.

Because the sentence begins with a subordinate clause:

În cazul în care stopul este defect, ...

After that introductory clause, Romanian normally uses a comma before the main clause:

..., mașina este respinsă.

So the comma is standard and expected here.

Yes. You could also say:

Mașina este respinsă în cazul în care stopul este defect.

That is also correct. The meaning stays basically the same.

The original order puts the condition first, which is very common in formal instructions and regulations.

In standard Romanian, yes, it is necessary here.

You need:

• stopul este defect
• mașina este respinsă

In informal speech, este is often shortened to e:

• stopul e defect
• mașina e respinsă

But you normally do not omit the verb completely.

A few useful ones:

• În: the â/î sound is a specifically Romanian vowel, not like a normal English i
• mașina: ș is pronounced like English sh
• respinsă: ă is a short central vowel, something like a weak uh
• cazul: the z is pronounced normally, like English z

So:

• ș = sh
• ă = a short unstressed uh
• î / â = a distinct Romanian vowel with no exact English equivalent

These diacritics matter both for pronunciation and correct spelling.