Learn Hardcore Spanish (Latin America): El mecánico explicó que, si el motor falla, primero revisa el aceite en el taller. - The mechanic explained that, if the engine fails, he first checks the oil in the workshop.

Que functions as a complementizer introducing a subordinate clause that contains the content of his explanation. In Spanish, to report what someone explains or says, you use verbo + que + subordinate clause. You do not add de before que; saying explicó de que would be wrong in this context.

Is the comma after que necessary, and why are there commas around si el motor falla?

The comma after que is optional and mainly stylistic. Standard Spanish normally doesn’t separate que with a comma when launching a subordinate clause (you’d write explicó que si...). Here, the writer set off si el motor falla with commas as a parenthetical conditional clause; you could drop the first comma and leave just ...si el motor falla, primero revisa... or omit both commas around the si clause.

Why is falla in the present indicative tense and not the future or subjunctive?

In Spanish si clauses for real or likely situations (open conditions), you always use the present indicative in the protasis. You use the subjunctive (imperfect subjunctive) only for hypothetical or unlikely events (e.g., si el motor fallara, revisaría...). And you never use the future in the si part; Spanish reserves the future for the main clause or avoids it altogether in these constructions.

Why does the main clause use revisa in the present tense instead of a future tense like revisará?

When describing habitual or general actions under real conditions, Spanish often uses the present tense in the apodosis. Here it means the first thing he checks (whenever the engine fails) is the oil. If you wanted to talk about a single future event, you could say primero revisará el aceite, but for a regular procedure, the simple present is more natural.

Why isn’t there a subject pronoun (like él) before revisa?

Spanish usually omits subject pronouns because the verb ending already indicates who performs the action. Since revisa is third person singular and the subject, the mechanic, is clear from the context, él is unnecessary. You could add él for emphasis or contrast, but it’s optional.

Could primero come after the verb as in revisa primero el aceite, and does it change the meaning?

Yes. Spanish word order is flexible: primero revisa el aceite and revisa primero el aceite are both correct. Placing primero before the verb slightly emphasizes the sequence; after the verb it’s more neutral. Neither change affects the basic meaning.

Does en el taller describe where he checks the oil or where the oil is?

En el taller modifies the verb revisa, indicating the location of the action: he checks the oil at the workshop. If you wanted to say the oil is in the workshop, you’d use something like el aceite que está en el taller.

Could I replace si el motor falla with si el motor se avería, and would that change the nuance?

Yes. Averiar(se) is another way to say to break down. Si el motor se avería means essentially the same as si el motor falla. Fallar is more common in everyday Latin American Spanish; averiar(se) can sound slightly more formal or technical, but both are correct.