Short answer. Yes. When an obligation is to deliver a specific, determinate thing, the law says that obligation includes delivering all its accessions and accessories, even if they were never separately mentioned in the agreement. A stereo installed in the car would ordinarily fall within that.
What the law says
The obligation to give a determinate thing includes that of delivering all its accessions and accessories, even though they may not have been mentioned.
Civil Code, Article 1166 — Accessions and Accessories. Read the full provision →
The rule for determinate things
The obligation applies specifically to a determinate thing, one that is particular and identified, such as this specific car, rather than a generic item that could be substituted with any equivalent. For that kind of obligation, delivery is understood to include not just the thing itself but also all its accessions and accessories, automatically, without needing to have listed them out.
Why the accessories don't need to be mentioned
The statute is explicit that this happens even though they may not have been mentioned. The obligor cannot argue that because the agreement only referred to "the car" without naming the stereo, the spare tire, or other fittings, those items were excluded. The law treats accessories as bundled with the principal thing as a default rule, not as something that has to be spelled out to apply.
What counts as an accession or accessory
Accessories are items attached to or associated with the principal thing that serve it or complete it, the kind of components a car owner would reasonably consider part of the vehicle rather than something separate. Whether a particular item, an aftermarket stereo, a roof rack, a spare part, actually qualifies as an accessory to the specific thing owed depends on how it relates to that thing, since the rule is about what naturally goes with the determinate object, not about every item that happens to be near it.
Timing matters too. The creditor is entitled to the thing as it stood when the obligation arose — the debtor cannot strip a car of its fittings between the agreement and the delivery and then hand over the shell. Article 1163 backs this up by requiring whoever must deliver a determinate thing to care for it with the diligence of a good father of a family until delivery.
What this means for you as the creditor
If someone owes you delivery of a specific car and it is handed over stripped of a stereo or other accessories it originally had, that is a shortfall in what was actually owed, not an acceptable substitute delivery. The default rule under the law is that you were entitled to the accessories along with the car itself, unless the parties had specifically agreed otherwise.
Two limits are worth knowing. The rule is a default, not a prohibition: parties who genuinely mean to keep an item out can say so, and an express exclusion agreed at the outset controls over the presumption. And the rule only bites where the object is determinate. If what is owed is a generic thing, any car of a given model, there is no particular object whose accessories can be identified, and the creditor's protection comes instead from the rule on quality in Article 1246.