If a man has intercourse with his wife during the day in Ramadaan whilst traveling, there is nothing wrong with that

He does not have to offer expiation and there is no sin on
him, because the traveler is permitted not to fast, but he has to make up
that day. 

The Standing Committee (10/202) was asked about the ruling on
a man who has intercourse with his wife during the day in Ramadaan when they
are traveling and not fasting. They replied: 

It is permitted for a traveler who is traveling during the
day in Ramadaan to break the fast, because Allaah says (interpretation of
the meaning): 

“and whoever is ill or on
a journey, the same number [of days which one did not observe Sawm (fasts)
must be made up] from other days”

[al-Baqarah 2:185]

It is permissible for him to eat, drink and have intercourse
so long as he is traveling. 

Shaykh Ibn Baaz was asked in Majmoo’ al-Fataawa
(15/307) about the ruling on a man who has intercourse during the day in
Ramadaan when he is fasting; is it permissible for a traveler to have
intercourse with his wife if he is not fasting? 

They replied: 

The one who has intercourse during the day in Ramadaan when
he is observing an obligatory fast has to offer expiation, i.e., the
expiation of zihaar (which is to free a slave; if that is not
possible then to fast for two consecutive months; if that is not possible
then to feed sixty poor persons). He must also make up that day, and repent
to Allaah for what he has done. But if he is traveling or sick, it is
permissible for him not to fast, and he does not have to offer any
expiation, and there is no sin on him, but he has to make up the day on
which he had intercourse, because those who are sick or traveling are
permitted not to fast and to have intercourse etc, as Allaah says
(interpretation of the meaning): 

“and whoever is ill or on
a journey, the same number [of days which one did not observe Sawm (fasts)
must be made up] from other days”

[al-Baqarah 2:185]

The ruling on a woman in
this case is the same as that on a man, if it was an obligatory fast then
she has to offer expiation and make up that day; if she was traveling or was
sick and fasting would be too difficult, then she does not have to offer
expiation. 

Shaykh Ibn ‘Uthaymeen was asked in Fataawa al-Siyaam
(344) about a man who had intercourse with his wife during the day in
Ramadan when he was traveling. 

He replied: There
is no sin on him for that, because the traveler is permitted to break his
fast and to eat, drink and have intercourse, so there is no sin on him and
he does not have to offer expiation. But he has to fast another day to make
up the day that he did not fast in Ramadaan. Similarly there is no sin on
the woman if she was travelling and not fasting on that day. But if she was
not traveling then it is not permissible for him to have intercourse with
her if she is observing an obligatory fast, because he will invalidate her
acts of worship, so she has to refuse.