Le voyant signale une défaillance du feu de croisement.

Here, voyant means a warning light or indicator light, especially on a car dashboard.

This is a good word to notice because voyant can mean different things in different contexts:

• in everyday French, un voyant / une voyante can mean a psychic or fortune-teller
• in car or technical language, un voyant usually means an indicator light

So in this sentence, it is definitely the dashboard warning light.

Le is the definite article, meaning the.

In instructions, manuals, and warning messages, French often uses the definite article when referring to a specific item being discussed, even if English might sometimes say a warning light. So Le voyant means the warning light, usually the one relevant in that situation.

If you said Un voyant, it would sound more like a warning light in a general sense, not a specific one.

Signale comes from the verb signaler, which means:

• to signal
• to indicate
• to point out
• to warn about

So Le voyant signale... means that the warning light indicates or alerts you to a problem.

Grammatically, signale is:

• present tense
• third person singular
• from signaler

So:

• je signale
• tu signales
• il / elle / on signale

Une défaillance means a failure, fault, or malfunction.

It sounds a bit formal or technical, which fits a dashboard or manual message well. It suggests that something is not functioning properly.

Compared with some related words:

• une panne = a breakdown, often a more obvious failure
• un défaut = a defect, flaw, or fault
• une défaillance = a malfunction/failure, often used in technical contexts

So une défaillance du feu de croisement sounds like a technical way to say that the low-beam light has failed or is faulty.

Because du is the required contraction of de + le.

French does this automatically:

• de + le = du
• de + les = des

So:

• de le feu → du feu

In this sentence, défaillance is followed by de to show what the failure concerns:

• une défaillance de le feu → incorrect
• une défaillance du feu → correct

Feu de croisement is the standard French term for a dipped headlight or low beam.

It is a fixed expression used in driving and vehicle vocabulary.

Related terms:

• feux de croisement = low beams
• feux de route = high beams
• feux de position = sidelights / parking lights

So feu de croisement is not something you translate word by word in a literal everyday way. It is a set technical term.

Yes, French can use both singular and plural, depending on what is meant.

Here, du feu de croisement is singular, which suggests a failure affecting one low-beam light or the low-beam system as a single item.

But you can also see:

• les feux de croisement = the low beams in general

For example:

• Allumez les feux de croisement. = Turn on the low beams.

So the singular here is normal, especially in a warning message about a specific fault.

Because de croisement is part of the fixed compound noun feu de croisement.

In French, many noun expressions are built like this:

• feu de route
• feu de croisement
• salle de bains
• verre de vin

The second noun often appears after de without its own article when it describes the type or function of the first noun.

So croisement is not being treated as a separate definite noun here. It is part of the name of the light.

Because they are doing two different jobs.

1. une défaillance du feu...

   • this de links défaillance to what has failed
   • it means a failure of the...

2. feu de croisement

   • this de is part of the fixed term naming the kind of light
   • it means something like low-beam light, not a separate possession structure

So the structure is:

[une défaillance] [du feu de croisement]

That whole second part means of the low-beam headlight.

No, it is very straightforward.

The structure is:

• Le voyant = subject
• signale = verb
• une défaillance du feu de croisement = direct object

So it is a normal subject + verb + object sentence.

That makes it a useful model:

• Le système détecte une anomalie.
• Le témoin indique un problème moteur.
• Le voyant signale une défaillance du feu de croisement.

Yes. French has several natural alternatives, depending on style and context.

For example:

• Le voyant indique une défaillance du feu de croisement.
• Le voyant signale un défaut du feu de croisement.
• Le feu de croisement est défaillant.
• Une ampoule de feu de croisement est défectueuse.

The original sentence sounds especially like a technical or manual-style warning message, which is why signale and défaillance fit well.