2011 Chevrolet Volt Owner's Manual - Page 347

Driving and Operating Turning the System On and Off The UFRPA system can be turned on and off by pressing the park assist button in the overhead console. 9-45 When the System Does Not Seem to Work Properly If UFRPA does not turn on due to a temporary condition, the message PARK ASSIST OFF displays on the DIC, and the light on the park assist button turns off. This can occur under the following conditions: . . An object was hanging out of the hatch during the last drive cycle. Once the attached object is removed, UFRPA will return to normal operation. The bumper is damaged. Take the vehicle to your dealer to repair the system. Other conditions may affect system performance, such as vibrations from a jackhammer or the compression of air brakes on a very large truck. . The park assist button lights up when the system is on and turns off when it has been disabled. The ultrasonic sensors are not clean. Keep the sensors free of mud, dirt, snow, ice, and slush. For cleaning instructions, see Exterior Care on page 10‑89. The vehicle was washed in cold weather. This may cause frost or ice to form in the park assist sensors. Keep the sensors free of frost or ice. . .