Do dealers have a 'secret warranty'?

Dear Terry,
A friend of mine who owns a Nissan Sentra that's a few years older than mine told me he got a problem fixed for free even though the car is out of warranty. He said there was "an unpublished service bulletin" to the dealer that extended the normal warranty for this particular problem. What's going on here, and how do I find out whether my car is covered, too?
-- Adolpho

Dear Adolpho,
What your friend is talking about are generally known as Technical Service Bulletins, or TSBs, which are sent to dealerships by manufacturers to alert them to problem areas that may be appearing on some cars.

They're not secret, but they're not widely disseminated either. Some TSBs tell the dealers the manufacturer will cover repairs outside of the original warranty period, but most do not. To find out about TSBs on your particular car, you can go to the dealer and ask to see the file, which the dealer should be willing to let you see. Some may sell you copies. Or, for a fee, AllData can provide TSBs on a wide range of vehicles.