POST not Inserting data into table

[fanboime]

Here is my ajax

$(".submit").click(function(){
		
		var vp = $("input#vehicle_plate").val();
		var vm = $("input#vehicle_model").val();
		var vt = $("input#vehicle_type").val();
		var da = $("input#date_acquired").val();
		var ad = $("input#assigned_driver").val();
		var dataString = 'vehicle_plate='+ vp + '&vehicle_model='+ vm + '&vehicle_type='+ vt + '&date_acquired='+ da + '&assigned_driver='+ ad;
		
		$.ajax({
		type: "POST",
		url: "process.php",
		data: dataString,
		success: function(){
		$('.success').fadeIn(200).show();
		$('.error').fadeOut(200).hide();
		}
		});
		return false;
		
		});

And here is my PHP where i pass my 'dataString'

<?PHP
include("db.classes.php");
$g = new DB();
$g->connection();

			if($_POST)
				{
					$vehiclePlate = $g->clean($_POST["vehicle_plate"],1);
					$vehicleModel = $g->clean($_POST["vehicle_model"],1);
					$vehicleType = $g->clean($_POST["vehicle_type"]);
					$assignedDriver = $g->clean($_POST["assigned_driver"],1);
					$ad = date('Y-m-d', strtotime($_POST["datepicker"]));

					$g->add($vehiclePlate, $vehicleModel, $vehicleType, $assignedDriver, $ad);
				}
$g->close();
?>

And here is my database query

public function add($vehiclePlate, $vehicleModel, $vehicleType, $assignedDriver, $ad)
		{
			$sql = "insert into vehicles(`vehicle_plates`,`DA`,`type`, `model`, `driver`) values('$vehiclePlate', '$ad', '$vehicleType', '$vehicleModel', '$assignedDriver')";
			
			if(!mysql_query($sql))
			{
				$this->error = mysql_error();
				return true;
			}
			
			else
			{
				return false;
			}
		}

the AJax is succesful but when i try and see the table in my databse the inserted row are al 'Undefined' what seems to be causing this?

[Strider64]

            var params = { vehicle_plate: vp, vehicle_model: vm, vehicle_type: vt, date_acquired: da, assigned_driver: ad }; // Set parameters

            var dataString = jQuery.param( params ); // Set parameters to correct AJAX format

            $.ajax({

               type:"post",

               url:"process.php",

               data: dataString,

               success:function(info){

                   $('#result').html(info); // Display the result back when saved:

               }

           });