Q:

Strict standards error, unable to solve

I tried but is not able to solve, checked and is getting the error on Strict Standard

Strict standards: Only variables should be passed by reference in ...

What am i doing wrong - how to correct it
$this->assignRef('prodDet'  , $prodDet);
$this->assignRef('CatName'  , $modelNewcar->getCatName($id));

$this->assignRef('nav'  , $nav);
$this->assignRef('CatList'  , $modelNewcar->loadMainCat($brand,$Carmodel,$minprice,$maxprice,$fuel_type));
    $this->assignRef('CatName'  , $modelNewcar->getCatName);
parent::display($tpl);

In below is the original code
function display($tpl = null)
{
    $mainframe =JFactory::getApplication();
    $option = JRequest::getCmd('option');

    $db         =JFactory::getDBO();
    $user               = JFactory::getUser();
    // Push a model into the view
    $model              = $this->getModel();
    $modelNewcar    = $this->getModel( 'product' );
    $id = JRequest::getVar('id','','default','int');
    $vid = JRequest::getVar('vid','','default','int');

    $prodDet = $modelNewcar->loadProduct($id,$vid);

    $this->assignRef('prodDet'  , $prodDet);
    $this->assignRef('CatName'  , $modelNewcar->getCatName($id));

    parent::display($tpl);
}

 function display($tpl = null)
{
    $db =JFactory::getDBO();
    $user               = JFactory::getUser();
    // Push a model into the view
    $model              =$this->getModel();
    $modelNewcar    =$this->getModel( 'category' );

    $brand = JRequest::getVar('brand','','default','int');
    $Carmodel = JRequest::getVar('model','','default','int');
    $minprice = JRequest::getVar('minprice','','default','int');
    $maxprice = JRequest::getVar('maxprice','','default','int');
    $fuel_type = JRequest::getVar('fuel_type','','default','');

        $this->assignRef('nav'  , $nav);
    $this->assignRef('CatList'  , $modelNewcar->loadMainCat($brand,$Carmodel,$minprice,$maxprice,$fuel_type));
        $this->assignRef('CatName'  , $modelNewcar->getCatName);
    parent::display($tpl);
}

A:

It's exactly what the error says. $this->assignRef() assigns a variable by reference.
For example:
$this->assignRef('CatName'  , $modelNewcar->getCatName($id));

Here you try to pass the function getCatName() to assignRef(). The solution would be to assign it to a variable first.
$catName = $modelNewcar->getCatName($id);
$this->assignRef('CatName'  , $catName);

Docs: http://php.net/manual/en/language.references.pass.php

