Tire Pressure Monitor Description and Operation
Tire Pressure Monitoring System Operation
The tire pressure monitor system warns the driver when a
significant loss or gain of tire pressure occurs in any of the 4
tires. It allows the driver to display the individual tire
pressures and their locations on the driver information center.
The system uses the body control module (BCM), driver
information center, instrument cluster, remote control door lock
receiver, tire pressure indicator module and a radio frequency
transmitting pressure sensor in each tire assembly. Each sensor has
an internal power supply.
When the vehicle is stationary, the sensors internal
accelerometer is inactive which puts the sensors into a Stationary
state. In this state the sensors sample tire pressure once every 30
seconds and do not transmit at all if the tire pressure does not
change. As vehicle speed increases, centrifugal force closes the
sensors internal roll switch, which puts the sensor into Wake and
then Drive mode. The remote control door lock receiver receives and
then sends the tire pressure and temperature data to the body
control module (BCM). The tire pressure indicator module sends
sensor ID and location data to the BCM . The BCM translates the
data contained in the tire pressure sensor radio frequency
transmissions into sensor presence, sensor mode, and tire pressure.
Once vehicle speed is greater than 40 km/h (25 MPH), the remote
control door lock receiver waits for the sensors to go into Drive
mode.
Each sensor has its own unique identification (ID) code which it
transmits as part of each RF message and must be learned into the
BCM memory. Once all 4 ID's have been learned and vehicle speed is
greater than 40 km/h (25 mph), the BCM continuously compares ID's
and pressure data in the received transmissions to the learned ID's
and pressures to determine if all 4 sensors are present and if one
or more tires are low. If the BCM detects a low tire pressure
condition, a variation in pressure between 2 tires on the same
axle, or a malfunction in the system, it will send a serial data
message to the instrument cluster requesting the appropriate tire
pressure monitor indicator illumination and also to display the
appropriate data message on the driver information center, if
equipped.
The sensors continuously compare their last pressure sample to
their current pressure sample and will transmit in Learn
Mode-Pressure Triggered if a 8.3 kPa (1.2 PSI) change in tire
pressure has been detected in either a Stationary or Drive state.
When the tire pressure system detects a significant loss, or gain
of tire pressure, the tire pressure monitor indicator icon is
continously illuminated on the instrument cluster and if equipped,
a check tire pressure type message is displayed on the driver
information center.
Both the indicator icon and driver information center message
can be cleared by adjusting the tire pressures to the recommended
kPa/PSI and driving the vehicle above 40 km/h (25 MPH) for at least
9 minutes.
If power is disconnected from the BCM or if the vehicle battery
is disconnected each tire pressure sensor ID is retained but all of
the tire pressure information is lost. Under these circumstances
the BCM cannot assume that the tire pressures were maintained over
an unknown period of time. Cars equipped with the driver
information center will display dashes and the scan tool will
indicate a default tire pressure value of 1020 kPa (148 PSI) for
each tire. To reactivate the sensors, the vehicle must be driven
above 40 km/h (25 MPH) for at least 9 minutes. When the sensors are
activated, the driver information center displays the current tire
pressures.
The BCM has the ability to detect malfunctions within the tire
pressure monitor system. In the event a DTC is set, the tire
pressure monitor indicator icon on the instrument cluster will
flash for 1 min. and then remain illuminated after the power switch
is turned ON and the instrument cluster bulb check has been
completed. Any malfunction detected will cause the driver
information center to display a service tire monitor system type
message.
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