I Faced the similar problem ,
This occurs manly due to error in query, try to run your query in php-myadmin or any other query runner and confirm that your query is working fine.
Even if our query syntax is correct other simple errors like leaving null or not mentioan a column that set as not null in table structure will cause this error.(This was the errror made by me)
As user1122069 explained the reason for $pdo->errorInfo() says nothing is wrong may be due to
$pdo->errorInfo() refers to the last statement that was successfully
executed.
Since $sql->execute() returns false, then it cannot refer to
that statement (either to nothing or to the query before)
Hopes this helps :)
