Like too many things today, it’s complicated. Generally an auto loan that you pay on time will help you because two important components of your credit score are your payment history (pay your bills on time) and the length of your credit history (longer is better).
Your payment history is the big one because it accounts for 35% of your score. Almost as important is the amount of debt you owe.
That accounts for 30% of your score, so if your loan is going to cause you to possibly over extend yourself, you may find your score dropping.
New credit and the type of credit you have are the other two components that make up your credit score and they account for 10% each.
Almost everybody needs to use credit at some time and it’s really important to use it when you need it but only when you need it. Make your payments on time and be careful with those credit cards. It’s OK to have them as long as you don’t use them too much. You may want to mortgage a home one day and if your potential lender sees a handful of new credit cards that you are actually using and a bunch of late payments to go along with them, your score is going to suffer and you’ll have a real hard time getting that loan that you really need.