Never admit anything to a dealer or anyone for that matter.
All GM vehicles have had black boxes since the late 90's primarily used for safety improvements (ie. Dual stage air bags). Overwhelming majority of vehicles have black boxes these days.
Knowing Your Rights
The data on a recorder is generally considered to be the car owner's personal property. Just as law enforcement can't access data on your computer without a search warrant, it can't access your car's EDR without one either. Attorneys and insurance companies can't typically access or use the data in a court case without the car owner's consent.
"In most states, the current vehicle owner, or their legal representative, can give or withhold permission to download EDR data," according to an FAQ on the Harris Web site. "Courts can subpoena EDR data through court orders and some states collect data under their existing laws governing crash investigations."
And you should check your automobile insurance as well as insurance policies can contain an "Agreement to Cooperate" clause. Such language allows an insurer access to EDR data if it wants it. However, some states have statutes that override these provisions. When a vehicle is sold, the EDR data becomes the property of the new owner.
That means that if a car is in a crash and is deemed a total loss by an insurance company, the insurer now owns the vehicle. The insurance company can then access the data on the EDR and could possibly use it in legal proceedings against the former owner, he says.