Vehicle expenses can be tagged under disallowable expenses if you're using Simplified Expenses, Darren.
Simplified expenses calculates your business expenses using a flat rate, rather than the actual cost. You'll have to calculate the vehicle expenses using the actual costs so it will be tagged under allowable expenses.
You can contact the HMRC's support to double check whether a business cost is an allowable expense.
Here are some references that you can use to easily determine allowable or disallowable expenses:
Once done, you can already categorise the transactions under the correct categories again.
Let us know if you need anything else.