Cruise control doesn't work 2006 Pontiac Grand prix

I have a 2006 grand prix and the cruise control recently stopped working.  there are no
lights on, but I was looking online and came across an article which said.

CRUISE CONTROL WON'T ENGAGE

The cruise control system will NOT engage if any of the following conditions are present:

* The transmission is in Park, Neutral, Reverse or Low gear
* The clutch is disengaged (clutch pedal depressed)
* The vehicle is traveling less and 25 to 30 mph (varies depending on year/make/model
of vehicle)
* The driver is holding his foot on the brake pedal (or the brake pedal switch is showing
a constant application of the brakes)
* There is no input from the vehicle speed sensor (which will also prevent the
speedometer from working)
* Engine speed and/or throttle position does not match the commanded position
* Electrical voltage to the PCM or other components in the system is too low (less than 9
volts)
* The ABS or Traction Control system has been active for more than two seconds (this
may vary depending the application)
* Vehicle speed is excessive (some cruise control systems are programmed NOT to
work above a certain maximum speed for safety reasons (typically 90 mph or faster)
* The system's self-diagnostics has detected a fault and set a code. This will deactivate
the system and prevent it from functioning until the fault is diagnosed and repaired.

So my first question is, even though my brake lights are still working normally, is it
possible that the brake pedal sensor could still be the culprit?  question 2, if the throttle
was to blame, how would i go about finding out?  Question 3,  I know i got a charging
system failure message a few weeks ago that went away on its own, but might indicate
the voltage is the culprit.  Do i just test the battery, and alternator to rule that out, or is
there something else i should be doing?  Thanks