Tire Pressure Module: Description and Operation
LOW TIRE PRESSURE WARNING SYSTEM (LTPW)
This system monitors tire pressure and provides warning via a low tire warning lamp and an audible tone(s) when a tire's pressure has fallen below
a predefined threshold. There are two thresholds, they are "Tire Pressure Low" and "Tire Pressure Critical". The system only operates when the
vehicle is moving above approximately 33 km/h (20 mph). Above this speed, the low tire pressure warning system will continuously monitor the
air pressure in all four tires. The low tire pressure warning system will alert the driver in the event the air pressure falls below a threshold in one or
more of the tires.
Each transmitter has a unique identity (ID) code. The identity code allows the module to indicate to the driver, through the low tire warning lamp,
that one of the tire has lost air pressure. The DRB can be used to tell which tire pressure sensor/transmitter has failed or sensed a low tire pressure
based on its identity.
Verification that the LTPW system is operational must be performed during a road test, since the system is only operational when the vehicle is
moving more than 33 km/h (20 mph). The DRB must not be connected during the road test. The DRB can be used following the road test to
monitor that signals were received by the module.
Refer to Maintenance and Service information for the required procedure to program the tire pressure sensor/transmitter and/or module.
Low Tire Pressure Warning Module
The LTPW module has a microprocessor controller that can monitor the transmissions from the transmitters at all times with the ignition on.
The LTPW module will store the last 32 transmissions from the tire pressure sensor/transmitters, however, they cannot be observed as they
occur with the DRB. There are three important values included in these transmissions. They are listed as: why the transmission was sent, from
which sensor it came from (LF, RF, RR, LR), and tire pressure. There are four reasons why the tire pressure sensor/transmitter will send
information to the LTPW module they are listed below:
Normal - This is the normal mode, the transmitter will start to transmit information to the LTPW module at approximately 33 km/h (20 mph)
and continue at a rate of approximately one transmission per minute.
1 PSI Change - If the pressure reading changes by more than one PSI between the normal sampling period of 30 seconds, the transmitter will
send this one PSI change information to the LTPW module within approximately 30 seconds.
Wake - This is the very first time that the tire pressure sensor/transmitter sends information to the LTPW module. This wake mode will occur
after the ignition is turned on and the vehicle has reached the start to operate speed of approximately 33 km/h (20 mph).
Program - When a magnet is placed next to the transmitter it closes a reed switch inside and forces the transmitter to send a signal to the
LTPW module. Placing a magnet next to the transmitter will normally be done for programming purposes when the LTPW module or the tire
pressure sensor/ transmitter is being replaced.
The module compares the transmitted tire pressure to the two pressure thresholds, low and critical. If the module determines that the tire
pressure transmitted is below the low or critical pressure, the module will signal the "Low Tire" lamp to come on.
The module performs diagnostic routines, stores diagnostic trouble codes and provides the appropriate lamp status to the BCM. When the
module determines that there is a fault, the Low tire pressure warning lamp signal circuit will be pulled low (grounded) and the BCM will turn
on the "Low Tire" lamp.
The LTPW module also stores its own identification number, each of the four transmitter identification numbers, module version and date of
LOW TIRE PRESSURE WARNING MODULE MODES
When the ignition is turned to the "run" position, the LTPW module performs a complete self-check of all electrical components in the system.
After the vehicle reaches a speed of approximately 33 km/h (20 mph), the module will perform a dynamic check of the tire pressure transmitters.
During the dynamic check, the vehicle speed may fall below 33 km/h (20 mph) but not for longer than one minute. The LTPW module will
confirm if the Radio Frequency (RF) transmissions from each tire pressure transmitters have been received.
If any component exhibits a trouble condition during the initialization or dynamic check, the LTPW module will set a DTC and illuminate the
"Low Tire" warning lamp. A fault can also occur if the LTPW module (after initialization) does not receive any transmissions from the
transmitter/sensor for six consecutive ignition cycles.
Diagnostic mode is considered to be any time that the DRB is hooked up to the DLC and is communicating with the LTPW module. In diagnostic
mode, the LTPW module does not monitor or accept the tire pressure sensor/transmitter signal. This means that you cannot read the tire pressure
sensor/transmitter transmission information while driving the vehicle with the DRB hooked up.