Well, checking that current sensor is free and easy. I filled the hole in mine with some black silicone and have been error free so far, my gas mileage has even improved.
If the sensor looks ok there were some other things that were pretty easy to check....make sure you don't have any light bulbs burned out (esp the 3rd brake light) and the connections to the bcm can get corroded, I pulled mine and cleaned them with contact cleaner then re-applied the dielectric grease. The brake light switch is also a possibility and that's not to hard to replace either, costs about $20 if I remember correctly.
On the more expensive/more difficult side I also read that a failing speed sensor or speed sensor wiring harness could cause similar problems.
If it's not one of the easy things you probably won't have much choice but to take it to the dealership and have them check it.. As 91parkave said it could also be a software issue.
Good Luck!
