The guarantor can't read, and no one has read the agreement. If he signs it, it should be considered as a true expression of will, so the signature is valid.

However, if the content of the contract known by the guarantor is significantly different from the actual content of the contract, it is a fraudulent signature and can apply to the court for cancellation. The agreement is invalid after it is revoked.

legal ground

Article 148 of the Civil Code: If a party commits a civil juristic act by fraudulent means against its true meaning, the defrauded party has the right to request the people's court or an arbitration institution to cancel it.

Article 149 If a third party commits fraud, causing one party to commit a civil legal act against its true meaning, and the other party knows or should know about the fraud, the defrauded party has the right to request the people's court or an arbitration institution to cancel it.