Do I declare company car on Self-Assessment when already paid for via Tax Code?

I am completing a self assessment for the Higher Income Benefit Tax Charge. I know the exact amount I owe in tax for this, and when I complete my self-assessment without adding in the car benefit amount, the calculation matches with my expectations. When I add the car benefit amount, the tax amount owed increases significantly, well beyond the amount of child benefit I was paid in the first place, so its obviously trying to tax me for the company car too, despite the fact that I pay for this via my adjusted tax code (990L). Will it cause me issues to submit my return without the car benefit amount given that I already effectively pay tax on this via PAYE?

Hi,
If you have received a P11D from your employer declaring a company car then this will need to be declared on your Self Assessment.
If once you file your tax return the balancing payment is higher than expected then if you contact HMRC we can review the calculation and amend if needed.
You can contact HMRC at:
Self Assessment: general enquiries.
Thank you.