2009 Jeep Grand Cherokee Owner's Manual - Page 350

348 STARTING AND OPERATING A tire pressure monitoring sensor is located in the spare wheel, if the vehicle is equipped with a matching full-size spare wheel and tire assembly. The matching full-size spare tire can be used in place of any of the four road tires. A low spare tire will not cause the Tire Pressure Monitoring Telltale Light to illuminate, a warning message to appear, or the chime to sound. The Tire Pressure Monitoring Telltale Light will illuminate in the instrument cluster, a "TIRE LOW PRESSURE" message will display in the instrument cluster for 60 seconds, and an audible chime will be activated, when one or more of the four active road tire pressures are low. Should this occur, you should stop as soon as possible, check the inflation pressure of each tire on your vehicle, and inflate each tire to the vehicle's recommended cold placard pressure value. The system will automatically update and the Tire Pressure Monitoring Telltale Light will extinguish, once the updated tire pressures have been received. The vehicle may need to be driven for up to 20 minutes above 15 mph (24 km/h) to receive this information. The Tire Pressure Monitoring Telltale Light will flash on and off for 75 seconds, and remain on solid when a system fault is detected. In addition, a "CHECK TPM SYSTEM" message will be displayed for 75 seconds when a system fault is detected, and a chime will sound. If the ignition key is cycled, this sequence will repeat, providing the system fault still exists. The Tire Pressure Monitoring Telltale Light will turn off when the fault condition no longer exists. A system fault can occur by any of the following: 1. Jamming due to electronic devices or driving next to facilities emitting the same Radio Frequencies as the TPM sensors. 2. Installing some form of aftermarket window tinting that affects radio wave signals.