2004 Mercury Sable

No drive in any gear position. Experienced a few little "jerks" on level ground and coasted into a parking spot. Fluid level is ok and fluid is not burned. Mechanical linkage is intact. Nothing happens when the gearshift is moved through all the positions. It has always shifted smoothly. I don't think it's the transmission itself; I think it's more likely an electronic control unit. I know it needs to be put on a diagnostic machine but it can't be driven to a shop. I was hoping that this may be such a common problem that you experts would know what needs to be done even without diagnostics.