Si le GPS ne fonctionne plus, suis les panneaux et évite de faire un deuxième détour.

Because this is a command in the tu form: suis les panneaux = follow the signs.

In French imperatives, the subject pronoun is usually left out:

• Tu suis les panneaux. = You follow the signs.
• Suis les panneaux ! = Follow the signs!

So suis here is the imperative form of suivre.

This is also an imperative, this time from the verb éviter.

With tu imperatives, regular -er verbs normally drop the final -s:

• Tu évites = you avoid
• Évite ! = avoid!

So:

• évite de faire... = avoid doing...

A useful comparison:

• Tu regardes → Regarde !
• Tu fermes → Ferme !
• Tu évites → Évite !

Because the verb pattern is éviter de + infinitive.

So French says:

• éviter de faire quelque chose = to avoid doing something

Examples:

• Évite de courir. = Avoid running.
• J’évite de manger trop tard. = I avoid eating too late.

So évite de faire un deuxième détour is grammatically normal French.

Ne ... plus means no longer or not anymore.

So:

• Le GPS ne fonctionne plus = The GPS no longer works / doesn’t work anymore

It wraps around the verb:

• ne fonctionne plus

This is a very common French negative pattern:

• Je ne sais plus. = I don’t know anymore.
• Il ne vient plus. = He doesn’t come anymore.

In everyday spoken French, the ne is often dropped:

• Le GPS fonctionne plus But in standard written French, ne ... plus is expected.

After si for a real possible condition, French normally uses the present tense, not the future.

So French says:

• Si le GPS ne fonctionne plus... = If the GPS stops working / if the GPS no longer works...

Not:

• Si le GPS ne fonctionnera plus... ❌

This is a very important rule:

• Si + present, then often present, future, or imperative in the other clause.

Examples:

• Si tu as faim, mange. = If you’re hungry, eat.
• Si elle vient, je partirai. = If she comes, I’ll leave.

Here the result clause is an imperative:

• Si le GPS ne fonctionne plus, suis les panneaux...

French often uses an article where English may not.

So le GPS is natural French, just as you often get:

• la voiture
• le téléphone
• le train

Even with abbreviations, French usually keeps the article:

• le GPS
• la TV
• le Wi-Fi (depending on usage/context)

English might sometimes say simply GPS, but French usually wants le GPS in a full sentence.

Both can mean second.

In many everyday contexts, deuxième and second are interchangeable:

• un deuxième détour
• un second détour

A traditional distinction is:

• deuxième = second in a series that may continue
• second = second and possibly the last of only two

But in modern usage, people often do not strictly follow that distinction. In this sentence, deuxième détour sounds completely natural.

Yes. In this context, les panneaux means the signs, especially road signs or direction signs.

The noun panneau can mean a sign, panel, or board depending on context. When talking about driving or directions, suivre les panneaux naturally means:

• follow the road signs
• follow the direction signs

So even though panneau can have several meanings, here the traffic/travel context makes it clear.

Yes, détour is a noun, and the French expression is faire un détour, literally to make a detour.

French often uses faire in expressions where English might use a single verb or a different construction.

So:

• faire un détour = take a detour / make a detour

In the sentence:

• évite de faire un deuxième détour = avoid taking a second detour

That is the normal idiomatic way to say it.

Because French can chain imperatives just like English:

• suis les panneaux
• et évite de faire un deuxième détour

This is the same idea as:

• Turn left and keep going
• Call me and wait outside

So the sentence gives two pieces of advice/instructions:

1. follow the signs
2. avoid making a second detour

You would use the vous imperative:

• Si le GPS ne fonctionne plus, suivez les panneaux et évitez de faire un deuxième détour.

Comparison:

• suis / évite = singular informal tu
• suivez / évitez = formal singular or plural vous

So the original sentence is clearly addressed to one person informally.