Cruise Control Inhibited

WARNING: This page is about a different car, the 2007 Hummer H2. However, it is still accessible from the selected car via links, so may be relevant.

The powertrain control module (PCM) inhibits the cruise control operation when any of the following conditions exist:

A Cruise Control System related DTC has been set.
The vehicle speed is less than 40 km/h (25 mph).
The vehicle is in PARK, REVERSE, NEUTRAL, or 1st gear.
The engine RPM is too low.
The engine RPM is too high.
The vehicle speed is too high.
The system voltage is not between 6 volts and 16 volts.
The Antilock Brake System/Traction Control System is active for more than 2 seconds.