on my '05 Impala there are no pressure sensors, they are reading the
speeds of the wheels through the ABS computer and throwing a light if
there is a mismatch.  Is it possible that you have one new tire and one
worn tire?

good luck

nate

Can I assume you've actually checked the pressure?  If it is down about 3 to
5 psi compared to the tire on the other side, the light will come on.

On my care, it does not read pressure, but the  computer counts the  wheel
revolutions and compares them.  The low tire will turn more revolutions than
the higher pressure tire and give the signal.
Assuming the pressure is OK, on my car (leSabre), you just hold in the reset
button for about 5 seconds and it will rest itself.  Yours may be different.

Document ID# 751368
2002 Chevrolet Monte Carlo
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Tire Pressure Monitor Description and Operation
The Tire Pressure Monitor (TPM) system alerts the driver when a large change
in the pressure of one tire exists while the vehicle is being driven. The
TPM system uses the Electronic Brake Control Module (EBCM), ABS wheel speed
sensor inputs, class 2 serial data circuit, and the Instrument Panel Cluster
(IPC) message center to perform the system functions. The EBCM contains the
software to calculate relative tire pressure differences. The software
requires approximately 30 minutes of straight line driving in each of the
three different speed ranges to complete the calibration process in order to
have full capability of detecting a tire pressure condition. The speed
ranges are as follows:

24-64 km/h (15-40 mph)
64-113 km/h (40-70 mph)
113-145 km/h (70-90 mph)
Each speed range has 2 modes of tire pressure detection:

Monitor Mode 1
Monitor Mode 2
The EBCM learns the tire pressure calibration for each speed range
independently. In Monitor Mode 1, the EBCM has only partially learned the
tire pressure calibration for the speed range and has limited detection
capability for a tire pressure conditions. In Monitor Mode 2, the EBCM has
fully learned the tire pressure calibration for the speed range and has full
detection capability for a tire pressure condition. Once the TPM system is
calibrated the EBCM monitors the ABS wheel speed sensor inputs, which will
all be the same as the learned calibration if the tire pressures stay the
same. If the pressure increases or decreases in a tire, so too will that
tires circumference and radius, which causes that wheel speed sensor input
to change. The EBCM recognizes this change in wheel speed as a tire pressure
condition. If the pressure in one tire becomes at least 69 kPa (10 psi)
higher or lower than the other three the EBCM commands the IPC message
center to display the LOW TIRE PRESSURE warning message via a class 2 serial
data circuit. This warning message is a re-configurable telltale and is
ranked as lowest priority and may not be displayed if a higher priority
message is requested at the same time. This message does not appear if more
than one tire has high or low pressure, or if the system is not calibrated
properly. The TPM system does not alert the driver to which tire is high or
low. To turn off the LOW TIRE PRESSURE warning message, refer to Tire
Pressure Monitor Reset Procedure .

Document ID# 679494
2002 Chevrolet Monte Carlo
--------------------------------------------------------------------------------
Tire Pressure Monitor Reset Procedure

Important
There are 3 different ways to reset the Tire Pressure Monitor (TPM) system.
After resetting, the TPM system requires up to 30 minutes of straight line
driving in each of the 3 speed ranges to complete the calibration process,
for further information, refer to Tire Pressure Monitor Description and
Operation . If the TPM system does not reset, or DTC C1245 remains current,
refer to Diagnostic System Check - Tire Pressure Monitoring .

Using the exterior lamp switch
Adjust all tire pressures to the recommended kPa/psi. Refer to Tire
Inflation Pressure Specifications in Maintenance and Lubrication, or to Tire
Placard in General Information.
Turn ON the ignition, with the engine OFF.
Cycle the exterior lamp switch from OFF to parking lamps 3 times within 5
seconds.
Use the scan tool in order to clear the TPM DTC.
Using the RDS radio, if equipped
Adjust all tire pressures to the recommended kPa/psi. Refer to Tire
Inflation Pressure Specifications in Maintenance and Lubrication, or to Tire
Placard in General Information.
Turn the ignition to ACC or ON, with the engine OFF.
Turn the radio OFF.
Press and hold the DISP button until SETTINGS is displayed.
Press the SEEK up or down arrows until TIRE MON is displayed.
Press the PREV or NEXT button to enter the submenu. RESET will be displayed.
Press the DISP button, A chime will sound and DONE will be displayed.
Scroll until EXIT is displayed.
Press the DISP button to exit the TPM reset mode. A chime will sound to
verify exit.
Use the scan tool in order to clear the TPM DTC.
Using the scan tool
Adjust all tire pressures to the recommended kPa/psi. Refer to Tire
Inflation Pressure Specifications in Maintenance and Lubrication, or to Tire
Placard in General Information.
Install the scan tool.
Turn ON the ignition, with the engine OFF.
With the scan tool select Special Functions.
Select TIM Reset.
Press the Reset soft key.
Use the scan tool in order to clear the TPM DTC.