function checkForm() {
    errMessage = "";

    if(document.getElementById('ddlTIVYear').selectedIndex == 0) {
        errMessage += "Please select a trade-in year.\n";
    }
    if(document.getElementById('ddlTIVMake').selectedIndex == 0) {
        errMessage += "Please select a trade-in make.\n";
    }
    if(document.getElementById('ddlTIVModel').selectedIndex == 0) {
        errMessage += "Please select a trade-in model.\n";
    }
    if(document.getElementById('ddlMake').selectedIndex == 0) {
        errMessage += "Please select a make.\n";
    }
    if(document.getElementById('ddlModel').selectedIndex == 0) {
        errMessage += "Please select a model.\n";
    }
    if (!IsZipcode(document.getElementById('customer_address_zip_input').value)) {
        errMessage += "Please enter a valid zip code.\n";
    }
    if(document.getElementById('ddlMileage')) {
    	if(document.getElementById('ddlMileage').selectedIndex == 0) {
        	errMessage += "Please select your Annual Mileage.\n";
    	}
    }

    if(errMessage != "") {
        errMessage = "Please Fix the following Field(s):\n\n" + errMessage;
        alert(errMessage); 
        return false; 
    } 
    
    return true; 
}