The contract hire and leasing firm, ranked 28th in this year's FN50, has written to its fleet customers informing them of the decision to close the business down.
The firm's managing director Colin Tourick has also left the company, which employs about 70 staff.
In a letter to customers Mel Goodliffe, commercial director, said: 'CitiCapital is not selling the portfolio and is committed to the continued management of all existing contracts.
'Initially this will be through the existing business unit but with a stated objective of appointing a third party management company and consequently there will be no change to the current billing and payment arrangements. A further announcement will be made if and when a suitable third party has been identified.'