Prowler V6-3.5L VIN G (2002)
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.
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 km/h (20 mph). When the vehicle attains a speed of approximately
33 km/h (20 mph), the 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 ID code allows the module to indicate to the driver, through the Low Tire Warning Indicator,
that one of the tires has lost air pressure. The DRBIII can be used to tell which tire pressure sensor/transmitter has failed or sensed a low tire
pressure based on its ID code.
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 DRBIII must not be connected during the road test. The DRBIII can be used following the road test to
check whether or not signals were received by the LTPW 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. 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:
Supervisory - 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.
6.9 kPa (1 psi) Change - If the pressure reading changes by more than 6.9 kPa (1 psi) between the normal sampling period of 30 seconds, the
transmitter will send this 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
vehicle has reached the start to operate speed of approximately 33 km/h (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" Pressure Warning Indicator to come on.
The module performs diagnostic routines, stores diagnostic trouble codes and provides the appropriate Indicator status to the BCM. When the
module determines that there is a fault, the low tire pressure signal circuit will be pulled low (grounded) and the BCM will turn ON the "Low Tire"
lamp.
The LTPW module also stores its own ID number, each of the four transmitter ID 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 6.9 kPa (1 psi) between transmissions when the wheel is rotating above 33 km/h (20 mph)).
The Tire Pressure Sensor/Transmitter unit consists of:
