Can my passenger sue me if I was not found at fault for an accident where the driver at fault had no insurance?

The question of fault or negligence is for a jury and is not determined by whether an officer issues a citation or not. The passenger could sue you, however, would have to prove that you were negligent and as a result of your negligence he/she suffered an injury. The lawyer would hopefully not sue you if the injuries are minimal and if he/she does not believe they could prove you were negligent. If you are served with a complaint contact your insurance carrier as they will likely defend any lawsuit brought against you.

Let me add a thought to what Adam correctly stated. Depending on how your auto insurance was set-up, or the auto insurance that applies to the car you were driving, there may be coverage available to you and your passenger that the lawyer would want to explore. If that is the case, do not interpret your passenger's looking into your insurance policy's coverage as an accusation that you did something wrong. If you have that kind of coverage, great, you were wise to get it as there are tons of instances when innocent people are hurt by people who have no insurance at all. And there are tons of time when innocent people are hurt by people who do not have enough insurance. For what it is worth, I recommend to all of my family and friends that they have at least $100,000/$3000,000 of UM/UIM coverage, and no less than $25,000 in PIP. These increases from the minimums are hugely valuable, and add very little to the monthly bill.