Totally agree with prior advice. Avoid a repo - voluntary or otherwise - at all costs if you want your credit score to survive.
Prior payment history won't matter a bit once the account is reported with a repo.
If you truly want out of this car, you need to sell it for at least what you still owe on it - check your payoff balance with the lender, it may be less than the "remaining account balance" since they won't earn interest after the payoff date. This should be fairly simple if you owe close to its blue book value - you can take it to CarMax or some similar place and get them to write you an offer and buy it from you, as long as the amount is going to overcome the payoff on the lien. If not, you'll have to put some cash toward the principal balance until the sales price meets or exceeds the remaining payoff balance.
Voluntary repo just means you're allowing your current lender to skip ahead in the repo process. Normally, that process is sue for repo/sequestration or otherwise issue a repo order - locate and repo/sequester the vehicle - sell it at auction - deduct auction gain from amount owed - sue for deficiency balance and take judgment. Voluntary repos just allow them to skip the first two teps and start with the auction. It does NOT simply let you out of the obligation for the original loan, and the amount you will have as a deficiency is governed only by the terms of your original contract - there are no allowances for age of the vehicle or mechanical problems. Quite the opposite, actually, since an older, less mechanically sound vehicle will bring less in an auction and leave you with a higher deficiency balance. It's not something to do unless you really have no other options and it will destroy your credit, especially your auto credit, for years.
