Cannot Get DLookup Function to work in Access 2013 -

i trying dlookup function work in access 2013, cannot work, heres have far :-

i have query called qry_vehicleoverview in query there 2 fields called vehiclenumber , datelastexam

i have form, there number of fields, 2 of them called vehicle1 , datelastexamv1, in datelastexam1 ! trying reference relevant exam based on vehicle1 qry_vehicleoverview field, when vehicle number added vehicle1 displays correct exam in datelastexam1

first of create combo box in form, called vehicle1 , referenced vehiclenumber qry_vehicleoverview

then created text box in form, , called lastexamvehicle1, in control source of field added dlookup function :-

=dlookup("[datelastexam]","qry_vehicleoverview","[vehiclenumber]=""" & [vehicle1].[text] & """")

then chose after update in event tab , selected code builder in here added :-

private sub lastexamvehicle1_afterupdate() me.lastexamvehicle1.requery end sub

but when run form, first of error of #type in field, when change value in vehicle1 eror changes #error

i create combo box in form, called vehicle1 , referenced vehiclenumber qry_vehicleoverview

if so, there no need dlookup have value.

set rowsource of vehicle1 qry_vehicleoverview , count of fields combobox 2 , use controlsource textbox:

=[vehicle1].[column](1) 

it automatically update.