Self-help is the part that shocks people, and the second sentence is the one they need. There is no hearing, usually no advance warning, and the lender does not have to prove anything to anyone before acting. What "without a breach of the peace" restrains is the manner of taking rather than the right to take: an agent who is confronted and leaves has generally stayed within it, and one who forces a locked garage or provokes a confrontation generally has not. Where the line falls is decided by state courts case by case, so the useful thing for a borrower to know is not the doctrine but the consequence, which is that once the vehicle is gone the argument has moved from whether it should have been taken to what is owed.
The obligation does not end with the property. The collateral is sold, and the reasonable expenses of retaking, holding and disposing of it are paid out of the proceeds before the debt is. Vehicles sell for less at auction than at retail, so the arithmetic frequently leaves a balance, and that balance is unsecured: the thing that secured it has gone. Published material on auto loans works that order of application, and the remaining balance is a subject in its own right. The belief worth naming is "they took the car, so we are square", which is acted on often and is generally wrong. Voluntary surrender does not change this. Handing the keys back avoids the cost and unpleasantness of a seizure, and it is still a repossession for every purpose that follows, including the sale, the shortfall and the credit reporting.
The first federal overlay is a debt collection rule with a very specific reach. 15 USC 1692f(6) makes it an unfair practice to take "or threaten to take any nonjudicial action to effect dispossession or disablement of property" where (A) there is no present right to possession of the property claimed as collateral through an enforceable security interest, (B) there is no present intention to take possession of it, or (C) the property is exempt by law from dispossession. Limb (A) is the one that reaches a repossession company acting on a debt the creditor has no enforceable lien for; limb (B) reaches the threat used purely as pressure by someone with no intention of following through; limb (C) reaches property state law puts out of reach. Published material on debt collectors and on the Fair Debt Collection Practices Act covers which businesses fall inside the statute's definitions, including why a repossession business is inside the Act for this one provision and outside it for the rest.
The second overlay is unconditional, and almost nobody knows it. Under 50 USC 3952(a) of the Servicemembers Civil Relief Act, where a servicemember entered into a contract before entering military service for the purchase of real or personal property, including a motor vehicle, or for the lease or bailment of such property, the property "may not be repossessed for such breach without a court order" during military service, and the contract may not be rescinded or terminated for a pre-service or in-service breach. The protection applies only where a deposit or an installment was paid by the servicemember before entering service (a)(2). It has teeth: 50 USC 3952(b) makes knowingly resuming possession in violation of it, or knowingly attempting to, punishable by a fine or up to a year's imprisonment. And at a hearing under the section a court may order repayment to the servicemember of prior installments or deposits as a condition of allowing the contract to be terminated, must stay the proceedings on application where the servicemember's ability to comply is materially affected by military service, and may make any other equitable disposition (a court's authority under 3952(c)).
What happens to the credit file and the debt afterward. The account is reported as a repossession, the balance that survives the sale continues to be owed and can be pursued like any other unsecured debt, and the creditor may charge the account off on its own books without cancelling it. Published material on charge-offs makes the last point in full. If a bankruptcy case is filed, the automatic stay generally halts collection and repossession while it is in place, which is a matter for the material on bankruptcy rather than for this page.