Welcome to the community!
You may need to expand on the context here a little bit - without the XML response body and the rest of the code you have in the Tests sandbox, it’s difficult to see what’s going on here.
I see you have
pm.response.vehicleheight in the expect statement, that would probably return
undefined so the test would pass.
pm.response.json() would parse a JSON body but as you mentioned XML this would probably fail with a script error, if used correctly.
Adding some logging here can help you out too -
console.log(pm.response.vehicleheight) would show you in the Postman Console what that value resolves too.
You could also take a look at this awesome tutorial from @vdespa - https://youtu.be/UjQpUNPCvy4
Without all the extra details though it’s hard to know for sure, it’s just making folks guess what’s going on rather than seeing what’s happening.