Jeep 2008 Grand Cherokee Owner's Manual page 335

matching full size spare tire is swapped with a low
pressure road tire, the next ignition key cycle will still
show the "Tire Pressure Monitoring Telltale Light" to be
ON, a chime to sound, a Low Pressure message to appear
in the EVIC, and the graphic display will still show the
low tire pressure value flashing. Driving the vehicle for
up to 10 minutes above 15 mph (24 km/h) will turn OFF
the "Tire Pressure Monitoring Telltale Light" as long as
none of road tires are below the low pressure warning
threshold. The EVIC will also display a "Spare Low
Pressure" text message, and the graphic display will
show a tire pressure value in place of the flashing low tire
pressure value.
NOTE: If your vehicle is not equipped with a matching
full size spare wheel and tire assembly, it does not have a
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 key cycle, the "Tire Pressure 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 vehicle for up to 10
minutes above 15 mph (24 km/h), the "Tire Pressure
Monitoring Telltale Light" will flash on and off for 75
seconds and then remain on solid. In addition, the EVIC
will display a CHECK TPM SYSTEM message for 3
seconds and then display dashes (- -) in place of the
pressure value. For each subsequent ignition key cycle, a
chime will sound, the "Tire Pressure Monitoring Telltale
Light" will flash on and off for 75 seconds and then
remain on solid, and the EVIC will display a CHECK
TPM SYSTEM message for 3 seconds and then display
dashes (- -) in place of the pressure value. Once you
repair or replace the original road tire, and reinstall it on
the vehicle in place of the spare tire, the TPMS will
update automatically.
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