Jeep 2012 Grand Cherokee Owner's Manual page 512

508 STARTING AND OPERATING
will automatically update and the Tire Pressure Monitor-
ing 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 "SERVICE TPM
SYSTEM" message may be displayed for approximately
5 seconds when a system fault is detected, and a chime
will sound. If the ignition switch 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.
3. Lots of snow or ice around the wheels or wheel
housings.
4. Using tire chains on the vehicle.
5. Using wheels/tires not equipped with TPM sensors.
NOTE: There is no tire pressure monitoring sensor in
the spare tire. The TPMS will not be able to monitor the
tire pressure. If you install the spare tire, in place of a
road tire, that has a pressure below the low-pressure
warning limit, upon the next ignition switch cycle, a
chime will sound, a "LOW TIRE PRESSURE" message
will be displayed in the instrument cluster for a mini-
mum of five seconds, and the Tire Pressure Monitoring
Telltale Light will turn ON. After driving the vehicle for
up to 20 minutes above 15 mph (24 km/h), the Tire
Pressure Monitoring Telltale Light will flash on and off