California Code, Civil Code - CIV § 1803.6

(a) A contract may provide that for each installment in defaultthe buyer shall pay a delinquency charge not in excess of one of the following amounts:

(b) Only one delinquency charge may be collected on any installment regardless of the period during which it remains in default. Payments timely received by the seller under a written extension or deferral agreement shall not be subject to any delinquency charge. The contract may also provide for payment of any actual and reasonable costs of collection occasioned by removal of the goods from the state without written permission of the holder, or by the failure of the buyer to notify the holder of any change of residence, or by the failure of the buyer to communicate with the holder for a period of 45 days after any default in making payments due under the contract.