Ettersom giret sitter fast, må girsystemet justeres.

Ettersom means since / as / because in the sense of giving a reason.

In this sentence, Ettersom giret sitter fast, må girsystemet justeres, it introduces the cause:

• because the gear is stuck

Compared with fordi:

• fordi is the most common straightforward word for because
• ettersom can sound a little more formal or written
• in many contexts, they can be translated the same way

So this sentence could also be written with fordi, but ettersom is perfectly natural.

This is because Norwegian main clauses follow the V2 rule: the finite verb comes in the second position of the main clause.

Here the sentence begins with a subordinate clause:

• Ettersom giret sitter fast = subordinate clause

Then comes the main clause:

• må girsystemet justeres

In the main clause, må is the finite verb, so it comes before the subject girsystemet.

That is why the structure is:

• Ettersom ... , må girsystemet justeres not
• Ettersom ... , girsystemet må justeres

This is very similar to sentences like:

• Når jeg kommer hjem, skal jeg spise.

Gir is the dictionary form, meaning gear.

Giret is the definite singular form:

• et gir = a gear
• giret = the gear

So the sentence is talking about a specific gear:

• the gear is stuck

This noun is neuter, which is why the indefinite article is et and the definite ending is -et.

Yes, it is a very common expression.

Literally:

• sitter = sits
• fast = stuck / fixed / tight

But together sitte fast means:

• to be stuck
• to be jammed
• to be lodged

So giret sitter fast means:

• the gear is stuck
• the gear is jammed

Norwegian often uses verbs like sitte, stå, and ligge in ways that sound more physical than English does.

Norwegian forms compounds very freely, much more than English does.

So:

• gir = gear
• system = system
• girsystem = gear system / transmission system
• girsystemet = the gear system

English often writes these as separate words, but Norwegian usually combines them into one word.

This is very normal in Norwegian:

• bilmotor = car engine
• sykkelhjul = bicycle wheel
• arbeidsdag = workday

Because Norwegian usually expresses the by adding an ending to the noun.

Here:

• et girsystem = a gear system
• girsystemet = the gear system

So the definite article is built into the noun itself.

English uses a separate word:

• the gear system

Norwegian often does not:

• girsystemet

Justeres is the -s passive form of justere.

• å justere = to adjust
• justeres = is adjusted / be adjusted / needs to be adjusted, depending on context

In this sentence:

• må girsystemet justeres means
• the gear system must be adjusted

This is a very common way in Norwegian to express passive meaning.

Compare:

• Vi justerer girsystemet = We adjust the gear system
• Girsystemet justeres = The gear system is adjusted / being adjusted

Because girsystemet is the thing receiving the action, not doing it.

Compare these two patterns:

1. Active:

   • Vi må justere girsystemet
   • We must adjust the gear system

2. Passive:

   • Girsystemet må justeres
   • The gear system must be adjusted

In your sentence, the passive is used because the focus is on the gear system, not on who will do the adjusting.

Usually it means must / have to / need to, but the exact tone depends on context.

Here:

• må girsystemet justeres means something like
• the gear system must be adjusted
• the gear system needs to be adjusted

In practical or technical contexts, må often sounds less dramatic than English must sometimes does. It often simply states necessity.

Because the sentence begins with a subordinate clause:

• Ettersom giret sitter fast

In standard written Norwegian, a subordinate clause that comes before the main clause is usually followed by a comma.

So:

• Ettersom giret sitter fast, må girsystemet justeres.

The comma helps mark the boundary between:

• the reason and
• the main statement

Yes. A very natural alternative is:

• Girsystemet må justeres ettersom giret sitter fast.

This keeps the same basic meaning.

The difference is mainly in emphasis:

• starting with Ettersom ... puts the reason first
• starting with Girsystemet må justeres ... puts the result or main point first

Both are grammatically correct.

A more everyday version might use fordi instead of ettersom:

• Fordi giret sitter fast, må girsystemet justeres.

Or even an active version:

• Siden giret sitter fast, må vi justere girsystemet.

That version adds vi (we) and sounds more direct:

• Since the gear is stuck, we need to adjust the gear system.

So the original sentence is natural, but slightly technical or formal in tone.