Santa Monica car-buying company TrueCar Inc. renewed a deal with insurance giant AAA, announcing Monday it will continue to power the auto club’s online auto-buying program.

The partnership allows more than 30 million AAA members to connect with dealers certified by TrueCar.

So-called affinity programs such as the one with AAA are the bread and butter of TrueCar’s business model, accounting for the vast majority of its revenue. One affinity group alone, San Antonio insurer USAA, accounts for 43 percent of TrueCar’s business, according to company filings. TrueCar does not report how much of its revenue comes from its partnership with AAA.

Shares of TrueCar fell 5 percent on Monday to close at $18.75.