Vika löytyi jarrusta.

Löytyä and löytää are related, but they are different verbs:

• löytää = to find
  
  • Mekaanikko löysi vian. = The mechanic found the fault.
• löytyä = to be found / to turn up / to be discovered
  
  • Vika löytyi. = The fault was found.

So Vika löytyi jarrusta focuses on the fault being discovered, not on the person who found it.

Not grammatically, no.

It is the past tense, 3rd person singular of löytyä, which is an intransitive verb. English often uses a passive here, but Finnish usually does not need one.

Compare:

• Vika löytyi jarrusta. = The fault was found in the brake.
  
  • focus on the fault turning up / being discovered
• Vika löydettiin jarrusta. = The fault was found in the brake.
  
  • true Finnish passive of löytää
  • focus on the action of finding, with the finder left unspecified

Both are possible, but löytyi is very natural in this kind of diagnostic context.

Because vika is the subject of the sentence.

In Vika löytyi jarrusta, the thing that was found is vika, so it appears in the nominative singular.

That is different from sentences where Finnish uses the partitive for an indefinite amount or an incomplete/partial idea. For example:

• Jarrusta löytyi vikaa.

This does not mean exactly the same thing. It means something like there was some fault/faultiness in the brake or fault was found in the brake, in a less countable, less specific way.

So:

• vika = a specific fault / the fault
• vikaa = some fault, faultiness, a non-specific amount of fault

Jarrusta is the elative case of jarru.

The elative ending is usually:

• -sta
• -stä

Its basic meaning is out of / from inside.

With verbs like löytyä and löytää, Finnish often uses the elative for the place something is found from:

• Avaimet löytyivät taskusta. = The keys were found in the pocket.
• Vika löytyi jarrusta. = The fault was found in the brake.

So even though English says in the brake, Finnish uses a form that is literally closer to from the brake.

Because jarrussa and jarrusta do different jobs.

• jarrussa = in the brake
  
  • this is the inessive case, often used for a static location
• jarrusta = from the brake / found in the brake
  
  • this is the elative case, often used with löytyä/löytää

So:

• Vika on jarrussa. = The fault is in the brake.
  
  • simple statement of location
• Vika löytyi jarrusta. = The fault was found in the brake.
  
  • discovery/result

This is a very common pattern in Finnish: one case for being somewhere, another for being found from somewhere.

It is the simple past (often called the imperfect in Finnish grammar).

More specifically:

• infinitive: löytyä
• present: löytyy = is found / can be found / turns up
• past: löytyi = was found / turned up

So:

• Vika löytyy jarrusta. = The fault is found in the brake / the fault is in the brake
• Vika löytyi jarrusta. = The fault was found in the brake

Yes. Finnish word order is fairly flexible.

You can also say:

• Jarrusta löytyi vika.

That is perfectly natural. The difference is mainly in focus:

• Vika löytyi jarrusta.
  
  • starts with vika, so the fault is the topic
• Jarrusta löytyi vika.
  
  • starts with jarrusta, so the brake is more in focus

English often has to keep a more fixed order, but Finnish can move parts around to highlight different information.

Because Finnish does not have articles.

So vika can mean:

• a fault
• the fault

Context tells you which one is meant.

That is why Finnish learners often feel that the noun looks a bit bare compared to English. This is normal.

It depends on context.

Jarru literally means brake, singular, but in real use it can refer to:

• one specific brake
• the relevant brake part being discussed
• sometimes the braking system more generally, if that is clear from context

If you clearly mean several separate brakes, you would use the plural:

• jarruista = from the brakes

So jarrusta does not automatically tell you exactly how large the physical part is. Context does that.

The difference is mainly discovery versus state.

• Vika on jarrussa.
  = The fault is in the brake.
  This simply states where the fault is.

• Vika löytyi jarrusta.
  = The fault was found in the brake.
  This adds the idea that someone investigated the problem and the fault turned out to be there.

So the second sentence is especially natural when talking about troubleshooting, diagnosis, or repair.