Autossa on vika, eli se pitää korjata.

Because autossa is the inessive case, which often means in something.

• auto = a car
• autossa = in the car

So Autossa on vika literally means There is a fault in the car.

Finnish often uses cases instead of separate prepositions like in, on, or from.

That is a very normal Finnish way to express possession or the presence of something somewhere.

The pattern is:

• [place / person in a case] + on + thing

So:

• Autossa on vika = There is a fault in the car
• literally: In the car is a fault

English prefers there is, but Finnish often just states the location first and then says what exists there.

Vika means fault, defect, or something wrong.

In this sentence, it means the car has some kind of problem, usually a mechanical or technical one.

Some similar words are:

• vika = a fault, defect
• ongelma = a problem
• häiriö = a malfunction / disturbance

So Autossa on vika suggests there is some fault in the car itself, not just a general problem related to it.

Finnish usually does not use articles like a, an, and the.

So vika by itself can mean:

• a fault
• the fault

depending on context.

Here, on vika is a natural way to say there is a fault or something is wrong. You do not need a word corresponding to English a.

Eli means that is, in other words, or sometimes so in the sense of explaining or restating something.

In this sentence:

• Autossa on vika, eli se pitää korjata.

the second part explains the consequence of the first:

• There is a fault in the car, so / that is to say it needs to be repaired.

It is a common spoken and written connector when you want to clarify or rephrase.

Here se refers to the car.

So:

• Autossa on vika = there is a fault in the car
• eli se pitää korjata = so it needs to be repaired

Even though vika is also possible as a nearby noun, in context se is understood as the car, because the natural thing to repair is the car.

In everyday Finnish, se is very commonly used for he/she/it/that, depending on context.

Yes, pitää has several meanings.

Two common ones are:

• pitää = to hold
• pitää = must / have to / need to

Here it has the second meaning.

So:

• se pitää korjata = it must be repaired / it needs to be repaired

This is a very common structure in Finnish:

• pitää + infinitive

For example:

• Minun pitää mennä = I have to go
• Auto pitää korjata = The car must be repaired

Because korjata is the infinitive used after pitää.

The structure is:

• pitää + infinitive

So:

• pitää korjata = needs to be repaired

Here:

• pitää is the conjugated verb
• korjata stays in the basic infinitive form

Compare:

• Minun pitää syödä = I have to eat
• Se pitää korjata = It must be repaired

Because Finnish often leaves the agent unspecified when it is not important.

Se pitää korjata focuses on the necessity of repair, not on who will do it.

It is similar to English:

• It needs to be repaired
• It must be repaired

If you wanted to say who repairs it, you could add that separately, for example:

• Mekaanikon pitää korjata se = The mechanic has to repair it

It is not a Finnish passive form grammatically, but in meaning it is often close to an English passive idea.

Literally:

• it must repair would be wrong in English

Natural English is:

• it must be repaired
• it needs to be repaired

So in Finnish, the infinitive korjata appears in its basic form, but the whole expression is understood as something that needs to happen to se.

Yes. Auto pitää korjata is also correct and very natural.

The difference is mainly in focus:

• Autossa on vika = There is a fault in the car
• Auto pitää korjata = The car needs to be repaired

In the original sentence, the first part introduces the problem, and the second part gives the consequence:

• There is a fault in the car, so it needs to be repaired.

Yes, Finnish word order is relatively flexible, but the original order is the most natural here.

• Autossa on vika sounds neutral and natural.
• Vika on autossa is also grammatical, but it emphasizes the fault or contrasts where the fault is.

Similarly:

• Se pitää korjata is neutral.
• Pitää korjata se is possible only in certain contexts, but it is not the normal basic order here.

So the sentence uses standard, neutral word order.

It works in both spoken and written Finnish.

A few notes:

• eli is common in both, especially when explaining something.
• se for it is completely normal.
• The structure is clear and standard, not slangy.

So this is a good everyday Finnish sentence that does not sound especially informal or especially formal.

Yes, depending on the nuance.

For example:

• Autossa on vika = There is a fault in the car
• Autossa on ongelma = There is a problem with the car
• Auto on rikki = The car is broken

These are similar, but not identical:

• vika focuses on a specific fault or defect
• ongelma is broader
• rikki means broken / out of order

So the original sentence sounds quite natural when talking about something being wrong with the car mechanically or technically.