Cadillac 2005 XLR Owner's Manual page 364

Each TPM sensor has a unique identification code that
is matched to one of the four tire positions on your
vehicle. The tire and wheel assembly positions are, left
front (LF); right front (RF); right rear (RR) and left
rear (LR). Any time you rotate your vehicle's tires or
replace one or more TPM sensors, the identification
codes will need to be matched to the new tire and wheel
position. The TPM matching process is performed in
a specific sequence and time limit. A special tool is also
required. See your dealer for service.
The SVC TIRE MONITOR message is displayed when
the TPM system is malfunctioning. For example,
one or more TPM sensors may be inoperable or
missing. See your dealer for service.
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The TPM system operates on a radio frequency subject
to Federal Communications Commission (FCC) Rules
and with Industry and Science Canada.
This device complies with Part 15 of the FCC Rules and
with RSS-210 of Industry and Science Canada.
Operation is subject to the following two conditions:
(1) This device may not cause harmful interference, and
(2) this device must accept any interference received
including interference that may cause undesired
operation of the device.
Changes or modifications to this system by other than
an authorized service facility could void authorization to
use this equipment.