It was a typo in the class method
public function updateRestaurant($fields = array(), $id = null) {
if (!$this->_db->update('rt_restaurant', $id, $fields, false)) {
throw new Exeption('There was a problem updating');
}
}
Also... the exception whas thrown because there was a error in de DB method I was selecting WHERE id = $ID
but in MySQL it was not called id but rest_id.