koukanbuhin ga todokimasita.

It is read:

こうかんぶひん が とどきました。

Breakdown:

• 交換部品 = こうかんぶひん
• が = が
• 届きました = とどきました

Natural pronunciation keeps the sentence flowing together, so it sounds like:

こうかんぶひんが とどきました。

交換部品 means replacement part or replacement parts, depending on context.

It is made of:

• 交換 = exchange, replacement
• 部品 = part, component

So together, it refers to a part used to replace a broken or faulty one.

が marks the grammatical subject of the sentence: the thing that arrived.

So in this sentence:

• 交換部品 = the replacement part
• が = is the thing that
• 届きました = arrived / has arrived

So the sentence is structured like:

The replacement part + arrived

Japanese often uses が when introducing or identifying what did the action, especially in a neutral statement like this.

Yes, but the nuance changes.

• 交換部品が届きました。
  = The replacement part has arrived.
  This simply reports what arrived.

• 交換部品は届きました。
  = As for the replacement part, it has arrived.
  This can sound more contrastive, like maybe other things have not arrived yet.

So が is the more straightforward choice if you are just announcing the arrival of the part.

届きました is the polite past form of 届く.

Dictionary form:

• 届く = to arrive, to reach, to be delivered

Polite past:

• 届きました = arrived / has arrived

This is made from:

• 届く → 届きます (polite non-past)
• 届きます → 届きました (polite past)

So the sentence is polite and appropriate for normal business or customer-service situations.

Because 届く and 届ける are different verbs.

• 届く = to arrive / to reach / to be delivered
  → intransitive
• 届ける = to deliver something
  → transitive

In this sentence, the replacement part is the thing that arrived, so 届く is correct.

• 交換部品が届きました。
  = The replacement part arrived.

If you said:

• 交換部品を届けました。
  that would mean
  = Someone delivered the replacement part.

So the original sentence focuses on the result: the part has reached its destination.

It can mean either in English, depending on context.

届く focuses on something reaching its destination. Because of that, English translations may vary:

• The replacement part arrived.
• The replacement part has been delivered.

If you are talking about mail, packages, or ordered goods, was delivered can sound very natural in English.
If you are just reporting that it has reached you, arrived also works well.

By itself, Japanese usually does not clearly mark singular vs. plural.

So 交換部品 could mean:

• a replacement part
• replacement parts

You determine that from context.

If the surrounding situation makes it clear that only one part was ordered, English will usually translate it as singular:

• The replacement part has arrived.

If several were expected, then:

• The replacement parts have arrived.

Japanese often leaves out information that is understood from context.

So 交換部品が届きました。 does not explicitly say:

• who received it
• where it arrived
• who sent it

Depending on the situation, it could imply:

• it arrived at the office
• it arrived at my house
• it arrived for the customer
• it arrived from the supplier

Japanese omits these details when they are already obvious to the listener or reader.

It is polite, but not extremely formal.

Because it uses ～ました, it is appropriate for:

• everyday polite conversation
• workplace communication
• emails
• customer service
• status updates

A casual version would be:

• 交換部品が届いた。

A more formal written/business style might add extra wording, for example:

• 交換部品が届きましたので、ご確認ください。
• 交換部品が到着しました。

So the original sentence is polite and very natural.

The basic order here is very natural:

• 交換部品
  • が
    • 届きました

Japanese often puts the verb at the end, so this follows the normal pattern.

You could change the sentence in certain contexts, but this is the standard and simplest way to say it. For a learner, it is best to think of the pattern as:

[thing] が [verb]

In this case: [replacement part] が [arrived]

No. Standard Japanese writing normally does not use spaces between words.

So the normal written form is:

交換部品が届きました。

Spaces are sometimes added only for learners, formatting, or readability. But in ordinary Japanese, you would write it without spaces.