Passing custom field value from Vehicle to Service request.

Hi,

I created a custom field called factory code on asset and vehicle record types. I am trying to create a Service request from Vehicle detail page . I need to bring in the custom field factory code to Service request page. I tried doing this but no luck

On the factory code custom field on Service request I set the deafult value to JoinFieldValue('<Asset>',[<AssetId>],'<stFactory_Code_ITAG>') but its not pulling over. Any suggestions please .....