Here's the breakdown:
* Repossession: This happens when you're behind on payments and the lender takes the car back. This is a *serious negative mark* on your credit report, significantly lowering your score.
* Voluntary Return (Surrender): If you're struggling to make payments, contacting the lender *before* you miss payments is crucial. You can negotiate a voluntary return. While this still negatively impacts your credit, it's generally less severe than a repossession. It might be reported as a "repurchase agreement" or similar, but the impact is less than a repossession. The lender might pursue you for the deficiency (the difference between the car's value and what you owe), but this is managed differently than a repossession.
* Trade-in: Trading the car in for a new one at a dealership avoids a negative mark on your credit report altogether, as long as the trade-in value covers your loan balance. However, you might have negative equity (owing more than the car is worth), requiring you to roll that debt into a new loan.
In short, proactively communicating with your lender and arranging a voluntary return is the key to minimizing the negative impact on your credit. Ignoring the problem and allowing a repossession will have far more severe consequences.