This article in the CCC about conscience is greatly mistaken

CCC 1800 which mistakenly says “A human being must always obey the certain judgment of his conscience.” This is a declarative, absolutist statement of the primacy of conscience using the terms “must …More
CCC 1800 which mistakenly says “A human being must always obey the certain judgment of his conscience.” This is a declarative, absolutist statement of the primacy of conscience using the terms “must” and “always” indicating no matter what. CCC1800 and 1790 are not Catholic teaching. They are in grievous error evidenced by the fact that they have no footnotes, no references, no documentation whatsoever. They are not found in any Magisterial document whatsoever. Following is the real Catholic teaching from two Papal Encyclicals and the Council of Trent that decisively condemn following conscience into intrinsic evil i.e. abortion/murder etc.
“The negative precepts of the natural law are universally valid. They oblige each and every individual, always and in every circumstance. It is a matter of prohibitions which forbid a given action semper et pro semper, without exception, because the choice of this kind of behaviour is in no case compatible with the goodness of the will of the acting …More
Denis Efimov
"A false conscience which is mistaken in things which are intrinsically evil commands something which is contrary to the law of God. Nevertheless, it says that what it commands is the law of God. ... one who follows such a conscience and acts according to it acts against the law of God and sins mortally. For there was sin in the error itself, since it happened because of ignorance of that which one …More
"A false conscience which is mistaken in things which are intrinsically evil commands something which is contrary to the law of God. Nevertheless, it says that what it commands is the law of God. ... one who follows such a conscience and acts according to it acts against the law of God and sins mortally. For there was sin in the error itself, since it happened because of ignorance of that which one should have known" (St. Thomas Aquinas, De Veritate, 17, 4, 3).

"sometimes the error of conscience does not have the power of loosing or of excusing, namely, when the error itself is a sin, such as when it proceeds out of ignorance of that which someone can know or is held to know, just as if he were to believe that simple fornication is a venial sin. And then, although he would believe himself to sin venially, nevertheless he would not sin venially, but mortally" (St. Thomas Aquinas, Quodlibet, 8, 6, 5).