That's the single most common myth about SQL debugging. "I need to see the query after preparation to be able to tell if an error occurred". The fact is, you don't, and I'll tell you why.
Once a query has been prepared, the placeholder can be considered as a valid string/integer. You don't care what's in it.
Also, if you set up PDO correctly, you'll get a detailed PDOException detailing the error you've had along with a complete backtrace of where the error happened, plus you get the error string from MySQL, which makes syntax errors very easy to find.
To enable PDO Exceptions and disable emulated prepares:
$pdo = new PDO("mysql:host=localhost;dbname=database_name", "user", "password");
$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$pdo->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
