Ich komme mit meinem, weil dein Auto nicht funktioniert.

Because mit always takes the dative case in German.

The implied noun here is Auto, which is neuter: das Auto.
So mein has to change to the dative singular neuter form:

• mein Auto = my car
• mit meinem Auto = with my car / in my car / by my car

That is why you get meinem.

German can leave out a noun if it is already clear from context. Here, meinem stands for something like meinem Auto.

So this sentence is basically a shorter version of:

Ich komme mit meinem Auto, weil dein Auto nicht funktioniert.

This is similar to English saying I’ll come with mine instead of I’ll come with my car, if the object is obvious.

It can be natural if the missing noun is obvious from context, especially in conversation.

However, if you want to sound clearer or more neutral, many learners should prefer:

Ich komme mit meinem Auto, weil dein Auto nicht funktioniert.

That full version is safer and more explicit. The shorter version works best when everyone already knows you are talking about cars.

Because dein Auto is the subject of the clause dein Auto nicht funktioniert.

Subjects are in the nominative case, so you use:

• dein Auto = your car

You would only use deinem Auto if the grammar required dative, for example after a dative preposition:

• mit deinem Auto = with your car

So in this sentence:

• mit meinem → dative, because of mit
• dein Auto → nominative, because it is the subject

Because weil introduces a subordinate clause, and in standard German the conjugated verb goes to the end of a subordinate clause.

So:

• Main clause: Ich komme mit meinem
• Subordinate clause: weil dein Auto nicht funktioniert

This verb-final pattern is very important in German:

• Ich bleibe zu Hause, weil ich krank bin.
• Er kommt später, weil er noch arbeitet.

So funktioniert moves to the end because of weil.

In German, subordinate clauses are normally separated by a comma. Since weil starts a subordinate clause, you put a comma before it.

So:

Ich komme mit meinem, weil dein Auto nicht funktioniert.

That comma is required in standard written German.

In this sentence, it most likely means something like with my car or more naturally in English, in my car / using my car.

German often uses mit with means of transport:

• mit dem Auto = by car
• mit dem Bus = by bus
• mit dem Zug = by train

So Ich komme mit meinem Auto is the normal way to say that you are coming using your own car.

Yes, but the meaning shifts a little.

• mit meinem Auto focuses on the car as the means of transport
• in meinem Auto focuses more on being inside the car

In this sentence, mit meinem Auto is the more standard and idiomatic choice.

Yes. funktionieren is commonly used for machines, devices, and vehicles to mean to work or to function.

So dein Auto funktioniert nicht means your car is not working.

You could also hear other verbs depending on context, but funktionieren is completely normal here.

Because German weil already means because, and it directly introduces the clause. You do not need an extra word like that.

So:

• weil dein Auto nicht funktioniert = because your car is not working

German simply connects the reason clause with weil.