If you have used this vehicle in the past for business purposes, just not claimed CCA on it, you will use the FMV of the vehicle the first year it was used for business purposes.
You are not required to claim CCA, and if you do not, then the value carries forward until if and when you do claim CCA. So the FMV of the vehicle, when it was first used for business purposes, is what will have carried forward until the current tax year. This number is your UCC.
If this is your first year of using the vehicle for business purposes, you will need to include your vehicle as an "addition" and use the Fair Market Value (FMV). You will not have a UCC amount.