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 manufacture.

LOW TIRE PRESSURE WARNING MODULE MODES
System Initialization
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
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.

Program Mode
The Program Mode enables the LTPW module to detect which wheel (LF, RF, RR, LR) is sending the signal. The module must learn each of the four tire pressure sensor/transmitters' identifications (ID). This transmitter ID "learning" is used so that if any other signals are being received by the LTPW module at this frequency, it won't be misinterpreted.

Programming is initially done at the assembly plant. If a LTPW module fails or one or more tire pressure sensor/ transmitter(s) fails, after replacement of the faulty component the LTPW module's diagnostic memory must be reprogrammed or cleared in order to relearn the transmitter ID.

The DRB can place the module in Program Mode. It is possible to reprogram only one tire pressure sensor/transmitter. To program a module place a magnet (special tool 8192) on the end of the LF wheel valve stem for approximately six seconds. The magnet will energize and close the Reed switch. With the Reed switch closed, the transmitter will transmit the identification (ID) and tire pressure to the module. After the module has learned that particular tire pressure sensor/ transmitter ID, the magnet should be moved to each of the other wheels in a clockwise direction. Hold the magnet at each wheel for six seconds before moving onto the next wheel. Exit the Program Mode. The module will store the locations of each transmitter ID. Using the DRB, verify that the module programming is complete by looking at the tire pressure sensor/transmitter ID's and pressure values.