Part 2A

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 kph (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.

The LTPW System consists of:
- Low Tire Pressure Warning Module
- 4 Tire Pressure Sensor/Transmitters
- Body Control Module (BCM)
- "Low Tire" Pressure Warning Indicator

The system operates by monitoring a Radio Frequency (RF) transmission from Tire Pressure Sensor/Transmitters located in each wheel, and integrated with the valve stem. The transmitter is powered by a battery located inside the assembly. To extend the life of the battery, the transmitter does not send a signal to the module at vehicle speeds below approximately 33 kph (20 mph). When the vehicle attains a speed of approximately 33 kph (20 mph) centrifugal force of the rotating wheel closes a Roll switch (inside the transmitter) that powers up the circuitry.

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 tires has lost air pressure. The DRBIII (R) 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 kph (20 mph). The DRBIII (R) must not be connected during the road test. The DRBIII (R) can be used following the road test to monitor that signals were received by the 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 DRBIII (R). 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:

Supervisor - This is the normal mode, the transmitter will start to transmit information to the LTPW module at approximately 33 kph (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 message that the tire pressure sensor/transmitter sends to the LTPW module. This wake mode will only occur after the ignition is turned ON and the vehicle has reached the start to operate speed of approximately 33 kph (20 mph).

Magnet - 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.

Tire Pressure Sensor/Transmitter
The system has four individual Tire Pressure Sensor/Transmitters, one mounted in each wheel. The valve stem is integral with the pressure sensor/ transmitter. Each tire pressure sensor/transmitter serves three functions:
1. It is used as a valve stem to inflate and deflate the tire.
2. It periodically measures tire pressure. (Approximately every 30 seconds).
3. It transmits the tire pressure value to the LTPW Module in the vehicle. (Approximately every 60 seconds or 30 seconds or more if the tire pressure changes by 1 PSI between transmissions when the wheel is rotating above (33 kph (20 mph)).

The Tire Pressure Sensor/Transmitter unit consists of:
- Three volt battery Pressure sensor
- 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 TRANSMITTER.

Battery
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 kph (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 kph (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 DRBIII (R).

NOTE: TIRE PRESSURE SENSOR/TRANSMITTER REPLACEMENT INVOLVES REMOVAL OF THE TIRE FROM THE WHEEL.

Roll Switch
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 kph (20 mph). When the vehicle is moving above 33 kph (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.

Integrated Circuit
The Integrated Circuit (IC) will sample the tire pressure once every 30-34 seconds if the vehicle is moving above 33 kph (20 mph). This IC also contains the tire pressure sensor/transmitter identity code.

Transmitter
The measured tire pressure value is transmitted when the vehicle speed is above approximately 33 kph (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 kph (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 OFF 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 DRBIII (R). If this type of failure occurred, the BCM DTC will have to be cleared as well.

Reed Switch
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 over 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 DRBIII (R).

Low Tire Pressure Warning Indicator and Warning Tone
The "Low Tire" Pressure Warning Indicator is located in the instrument cluster and is displayed as "Low Tire". The indicator is used to inform the driver that one or more of the tires have low air pressure. The "Low Tire" indicator is controlled by the LTPW module indirectly through the Body Control Module (BCM). The BCM controls the "Low Tire" indicator by communicating with the instrument cluster via the CCD Bus. The instrument cluster controls the "Low Tire" indicator by directly grounding the indicator. When the ignition is turned ON, the LTPW module grounds the LTPW Indicator Signal Circuit for two seconds. The BCM will then illuminate the "Low Tire" indicator 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" indicator 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 kph (20 mph). When the LTPW module senses that pressure is below one of two calibrated thresholds, Low pressure or Critical pressure the LTPW Module will indirectly operate the "Low Tire" indicator and the chime tone through the BCM.

If the tire pressure is low, the low tire pressure warning indicator 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" indicator at the same rate and operate the chime tone for one single long tone.

If the tire pressure is critical, the low tire pressure warning indicator signal circuit will be pulsed to ground by the LTPW module for one second ON then one second OFF. The BCM will then illuminate the "Low Tire" indicator and sound the chime tone at the rate of one second OFF and one second ON.

The module will continue to pulse to ground the low tire pressure warning indicator signal circuit until the ignition is turned OFF, or the tire pressure transmitter(s) transmits a pressure above the calibrated threshold.

NOTE: A LOW TIRE PRESSURE CONDITION DOES NOT SET A DTC. THE DRBIII (R) CAN BE USED TO VIEW THE LAST 32 TRANSMISSIONS IN THE MODULE'S MEMORY AND TO CONFIRM WHICH TIRE WAS REPORTING THE LOW PRESSURE CONDITION.

If more than one condition is set at the same time, the LTPW module will prioritize how the "Low Tire" lamp will be illuminated. The priority rankings are listed below.

Critical Pressure - Lamp flashes at one second ON and one second OFF
Low Pressure - Lamp flashes at two seconds ON and two seconds OFF
LTPW Module Failure (DTC) - Lamp on steady
Tire Pressure Sensor/ Transmitter (DTC) - Lamp on steady
Less than four transmitter IDs learn - Lamp on steady
Critical tire pressure is zero - Lamp on steady
Normal tire pressure - No lamp
No faults - No lamp

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 module.

Operational Mode
After the vehicle reaches a speed of approximately 33 kph (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 kph (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 indicator. 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 DRBIII (R) 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 DRBIII (R) hooked up.

Program Mode
The Program Mode enables the LTPW module to record each wheel transmitter ID in the following order (LI, RI, RR, LR) in memory. 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 must be reprogrammed to learn the transmitter ID.

The DRBIII (R) 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) over 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 on to the next wheel. Exit the Program Mode. The module will store the locations of each transmitter ID. Using the DRBIII (R), verify that the module programming is complete by looking at the tire pressure sensor/transmitter ID's and pressure values.