Jeep Grand Cherokee Owner's Manual page 173

The tire pressure will vary with temperature by
about 1 psi (7 kPa) for every 12°F (–11°C). This
means that when the outside temperature de-
creases, the tire pressure will decrease. Tire
pressure should always be set based on cold
inflation tire pressure. This is defined as the tire
pressure after the vehicle has not been driven
for at least three hours, or driven less than
1 mile (1.6 km) after a three-hour period. Refer
to the "Tires – General Information" in this
section for information on how to properly
inflate the vehicle's tires. The tire pressure will
also increase as the vehicle is driven - this is
normal and there should be no adjustment for
this increased pressure.
The TPMS will warn the driver of a low tire
pressure if the tire pressure falls below the low
pressure warning threshold for any reason,
including low temperature effects, or natural
pressure loss through the tire.
The TPMS will continue to warn the driver of low
tire pressure as long as the condition exists,
and will not turn off until the tire pressure is at or
above recommended cold tire pressure. Once
the "TIRE LOW PRESSURE" message appears,
the tire pressure must be increased to the
recommended cold tire pressure in order for
the "TIRE LOW PRESSURE" message to be
turned off. The system will automatically update
and the "TIRE LOW PRESSURE" message will
turn off 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.
For example, your vehicle has a recommended
cold (parked for more than three hours) tire
pressure of 33 psi (227 kPa). If the ambient
temperature is 68°F (20°C) and the measured
tire pressure is 28 psi (193 kPa), a temperature
drop to 20°F (-7°C) will decrease the tire pres-
sure to approximately 24 psi (165 kPa). This tire
pressure is sufficiently low enough to display
the "TIRE LOW PRESSURE" message. Driving
the vehicle may cause the tire pressure to rise
to approximately 28 psi (193 kPa), but the
"TIRE LOW PRESSURE" message will still dis-
play. In this situation, the "TIRE LOW PRES-
SURE" message will turn OFF only after the
tires have been inflated to the vehicle's recom-
mended cold tire pressure value.
CAUTION!
• The TPMS has been optimized for the
original equipment tires and wheels. TPMS
pressures have been established for the
tire size equipped on your vehicle. Unde-
sirable system operation or sensor damage
may result when using replacement equip-
ment that is not of the same size, type,
and/or style. Aftermarket wheels can cause
sensor damage. Do not use aftermarket tire
sealants or balance beads if your vehicle is
equipped with a TPMS, as damage to the
sensors may result.
• After inspecting or adjusting the tire pres-
sure always reinstall the valve stem cap.
This will prevent moisture and dirt from
entering the valve stem, which could dam-
age the Tire Pressure Monitoring Sensor.
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