Fejlkoden viser funktionsfejlen.

Because Danish usually adds the definite article to the end of the noun.

• fejlkode = error code

• fejlkoden = the error code

• funktionsfejl = functional error / malfunction
• funktionsfejlen = the functional error / the malfunction

So the sentence uses two definite nouns: the error code and the malfunction.

Danish forms compound nouns very freely, much like German. Where English often uses two words, Danish often uses one:

• fejl = error
• kode = code
• fejlkode = error code

The same thing happens in:

• funktionsfejl = function error / malfunction

This is very normal in Danish technical language.

That s is a linking element inside the compound noun.

Break it down like this:

• funktion = function
• funktionsfejl = function error / malfunction
• funktionsfejlen = the function error / the malfunction

The s does not mean possession here. It is just a common way of connecting parts of a compound noun in Danish. You will see this a lot:

• arbejdsdag = workday
• livsglæde = joy of life
• funktionsfejl = function error

So funktions- is the compound form used before fejl.

Viser is the present tense of vise, which means to show, to display, or sometimes to indicate.

• at vise = to show
• viser = shows / is showing

In Danish, the present tense is the same for all persons:

• jeg viser = I show
• du viser = you show
• den viser = it shows
• de viser = they show

So there is no change like English show/shows except that Danish uses one form for everyone.

This is the normal word order for a main clause:

subject + verb + object

• Fejlkoden = subject
• viser = verb
• funktionsfejlen = object

Danish main clauses follow the V2 rule, which means the finite verb is in second position. Here, the subject is first, so the verb naturally comes next.

It can suggest any of those, depending on context. In a technical sentence like this, viser often means:

• shows
• displays
• indicates

So the sentence could imply that the error code reveals what the malfunction is. In technical English, indicates might sometimes sound slightly more natural, but viser itself is completely normal Danish.

Because Danish usually does not use a separate the before a noun when the noun stands alone in its definite form. Instead, the definiteness is attached to the noun itself:

• en fejlkode = an error code

• fejlkoden = the error code

• en funktionsfejl = a malfunction
• funktionsfejlen = the malfunction

A separate definite word is used mainly when there is an adjective:

• funktionsfejlen = the malfunction
• den alvorlige funktionsfejl = the serious malfunction

So in your sentence, no separate word for the is needed.

Yes. In this sentence it is being treated as a singular countable noun:

• en funktionsfejl = a malfunction
• funktionsfejlen = the malfunction

That means the sentence is talking about one specific malfunction. In other contexts, Danish could also talk about several:

• funktionsfejlene = the malfunctions

Yes, especially in a technical or mechanical context. It sounds like something you might read in documentation, diagnostics, or software/hardware messaging.

It is fairly compact and formal. In more everyday language, a speaker might choose a more explanatory wording, but the sentence itself is grammatical and natural in technical Danish.

A rough English-friendly guide would be:

fyle-koh-den VEE-ser fungk-TSYOHNS-fyle-en

A few notes:

• fejl sounds roughly like file, but not exactly.
• viser has stress on the first syllable: VEE-ser
• funktions- contains a clear ts sound
• fejlen again contains that fejl sound

As usual with Danish, the real pronunciation is softer and more reduced than the spelling suggests, but this rough guide can help you get started.