Sandra, even though your lender already looked at your credit and issue a pre-approval, it doesn't mean your new auto loan is going to fly under the radar. First, the credit that was initially pulled is good for 90 days, so of for whatever reason you don't find a house, go into contract, submit a mortgage application along with all necessary documents AND close by the time 90 days are up, THEY WILL PULL ANOTHER CREDIT REPORT. Even if you do close within the 90 days, most lenders will run a comparison report which serves the sole purpose of seeing if you took on any new debt.
We don't know the details of your financial situation. Generally taking on a new auto loan can have a negative affect on your chances of getting a mortgage. But it's very possible that you don't have much or any liabilities and you can indeed take on modest auto loan. This is something you should speak to your loan officer about. Your Loan Officer can run the numbers and instantly know how much auto loan you can take on, if any, and still qualify for your mortgage.
Senior Loan Officer
STERLING NATIONAL BANK
310 Crossways Park Drive
Woodbury, NY 11797