The Tire Pressure Sensor/Transmitter unit consists of:
Three volt battery
Roll switch (speed activated)
Reed switch (magnet activated)
Radio Frequency (RF) transmitter.
CAUTION: Inflatable tire sealants for fixing a slow leak or flat tire should be avoided as the sealant will clog the pressure sensing hole in the
The three volt Lithium battery is used to power up the Integrated Circuit (IC) board in the Tire Pressure/Sensor Transmitter unit. The battery
is only used above 33 km/h (20 mph) to improve its useful service life. The transmitters are capable of notifying the module when a battery is
low. Upon receiving a low battery message, the module will track the status of the battery for 3 consecutive ignition cycles. (An ignition cycle
is defined as: ignition on, and left on for at least 15 minutes, and vehicle speed above approximately 33 km/h (20 mph) long enough for the
module to receive a transmission from each transmitter.) If the battery is still low after 3 consecutive ignition cycles, the LTPW Module will
set a Diagnostic Trouble Code (DTC). The battery is a non-serviceable part and must be replaced with a complete Tire Pressure
Sensor/Transmitter unit. The new tire pressure sensor/transmitter must be programmed using the DRB.
NOTE: Tire pressure sensor/transmitter replacement involves removal of the tire from the wheel.
There is an integral roll switch that must be closed before the transmitter is powered up. This roll switch is open when the vehicle is stopped or
below approximately 33 km/h (20 mph). When the vehicle is moving above 33 km/h (20 mph) centrifugal force will close the roll switch,
powering up the Tire Pressure Sensor/Transmitter unit.
NOTE: The transmitter takes about 2 minutes to fall asleep after the roll switch opens.
The Integrated Circuit (IC) will sample the tire pressure once every 30-34 seconds if the vehicle is moving above 33 km/h (20 mph). This IC
also contains the tire pressure sensor/transmitter identity code.
The measured tire pressure value is transmitted when the vehicle speed is above approximately 33 km/h (20 mph), every 60-68 seconds or if
the pressure drops one or more pounds per square inch (PSI) between sampling periods. It is important to note that not all the tire pressure
sensor/transmitters will start to transmit at the same time. Due to manufacturing tolerances some transmitters may start to operate with speeds
as low as 16 km/h (10 mph).
The module continuously monitors and records the last 32 transmissions that it receives. When the module notices that one of the tire pressure
sensor/transmitters has not sent its information within the last 32 transmission windows, it will set a Diagnostic Trouble Code (DTC) and turn
the "Low Tire" lamp on steady. If the transmitter begins transmitting again, the module will shut oft the "Low Tire" lamp, however, the
transmitter ID and number of occurrences are stored. This data is in the module memory and can be erased using the DRB. If this type of
failure occurred, the BCM DTC will have to be cleared as well.
A magnet is used to close the Reed switch. The only time that the Reed switch is used is when the module is programmed. When a magnet is
placed on the end of the valve stem, it will close the Reed switch. With the Reed switch closed the transmitter will send its ID and tire pressure
to the module. The ID and tire pressure can be read using the DRB.
Low Tire Pressure Warning Lamp And Warning Tone
The "Low Tire" Pressure Warning Lamp is located in the instrument cluster and is displayed as "Low Tire". The lamp is used to inform the
driver that one or more of the tires have low air pressure. The "Low Tire" lamp is controlled by the LTPW module indirectly through the Body
Control Module (BCM). The BCM controls the "Low Tire" lamp by communicating with the instrument cluster via the CCD Bus. The
instrument cluster control the "Low Tire" lamp by directly grounding the lamp. When the ignition is turned on, the LTPW module grounds the
LTPW Lamp Signal Circuit for two seconds. The BCM will then illuminate the "Low Tire" lamp for 2 seconds signifying that the system is
operational. If the BCM does not sense that the LTPW module has provided a ground path after initial ignition on, or the LTPW module has
set a DTC and is keeping the Low Tire Pressure Warning Signal Circuit grounded, the BCM will set the "Tire Pressure Input Circuit Fault"
DTC. The BCM will turn the "Low Tire" lamp on and it will stay on, signifying a problem with the LTPW system.
The transmitters will only send out tire pressure information when the vehicle speed is above approximately 33 km/h (20 mph). When the
transmitter senses that pressure is below one or two calibrated thresholds, Low pressure or Critical pressure, the LTPW module will set a DTC,
and will indirectly operate the "Low Tire" lamp and the chime tone through the BCM.
If the tire pressure is low, the low tire pressure warning lamp signal circuit will be pulsed to ground by the LTPW module for two seconds on
and then two seconds off. The BCM will then illuminate the "Low Tire" lamp at the same rate and operate the chime tone for one single long