Jeep Grand Cherokee 2012 Owner's Manual page 471

If the ignition switch is cycled, this sequence will repeat,
providing the system fault still exists. If the system fault
no longer exists, the Tire Pressure Monitoring Telltale
Light will no longer flash, the SERVICE TPM SYSTEM
message will not be present, and a pressure value will be
displayed instead of dashes. 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.
The EVIC will also display a SERVICE TPM SYSTEM
message for a minimum of five seconds when a system
fault is detected possibly related to the trigger compo-
nent an incorrect sensor location fault. In this case, the
SERVICE TPM SYSTEM message is then followed by a
graphic display, with pressure values still shown. This
indicates the pressure values are still being received from
the TPM Sensors but they may not be located in the
correct vehicle position. However, the system still needs
to be serviced as long as the SERVICE TPM SYSTEM
message exists.
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, the Tire Pres-
sure Monitoring Telltale Light will remain ON, a chime
will sound, and the EVIC will still display a "flashing"
pressure value in the graphic display. After driving the
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