815 ILCS 375/18
Each person, other than a seller or holder, who signs a retail installment contract may be held liable only to the extent that he actually receives the motor vehicle described or identified in the contract, except that a parent or spouse or any other person listed as an owner of the motor vehicle on the Certificate of Title issued for the motor vehicle who co-signs such retail installment contract may be held liable to the full extent of the deferred payment price notwithstanding such parent or spouse or any other person listed as an owner has not actually received the motor vehicle described or identified in the contract and except to the extent such person other than a seller or holder, signs in the capacity of a guarantor of collection.
The obligation of such guarantor is secondary, and not primary. The obligation arises only after the seller or holder has diligently taken all ordinary legal means to collect the debt from the primary obligor, but has not received full payment from such primary obligor or obligors, or after the primary obligor has become insolvent, or service of summons cannot be obtained on the primary obligor, or it is otherwise apparent that it is useless to proceed against the primary obligor.
No provisions in a retail installment contract obligating such guarantor are valid unless:
"I hereby guarantee the collection of the above described amount upon failure of the seller named herein to collect said amount from the buyer named herein."; and
"EXPLANATION OF GUARANTOR'S OBLIGATION
You ........... (name of guarantor) by signing the retail installment contract and this document are agreeing that you will pay $......... (total deferred payment price) for the purchase of ........... (description of goods or services) purchased by ............ (name of buyer) from ........... (name of seller).
Your obligation arises only after the seller or holder has attempted through the use of the court system to collect this amount from the buyer.
If the seller cannot collect this amount from the buyer, you will be obligated to pay even though you are not entitled to any of the goods or services furnished. The seller is entitled to sue you in court for the payment of the amount due."
The instrument must be printed, typed, or otherwise reproduced in a size and style equal to at least 8 point bold type, may contain no other matter (except a union printing label) than above set forth and must bear the signature of the co-signer and no other person. The seller must give the co-signer a copy of the retail installment contract and a copy of the co-signer statement.
815 ILCS 375/18