Dodge ZB 2005, Service Manual

Page: 1398 / 1873

3.12 TIRE PRESSURE MONITORING
SYSTEM (TPMS)
This system monitors tire pressures and provides
warning via a ‘‘Lo Tire’’ LCD message and an
audible warning alert when a tire pressure has
fallen below a predefined threshold. There are two
thresholds; they are ‘‘Tire Pressure Low’’ and ‘‘Crit-
ical Tire Pressure.’’ The system only operates when
the vehicle is moving above 33 km/h (20 mph.)
Above this speed, the Tire Pressure Monitoring
system continuously monitors the air pressure in
all four tires. The Tire Pressure Monitoring system
will alert the driver in the event the air pressure
falls below a threshold in one or more of the tires.
The TPM system consists of:
– Tire Pressure Monitor Module
– Four Tire Pressure Sensor/Transmitters
– Body Control Module (BCM)
– ‘‘Lo Tire’’ LCD message (Instrument Cluster)
The system operates by monitoring a radio fre-
quency (RF) transmission from the Tire Pressure
Sensor/Transmitters located in each wheel, and
integrated with the valve stem. A battery located
inside the assembly powers the transmitter. To
extend the life of the battery, the transmitter, when
below 33km/h 20mph will continue to transmit for
fifteen minutes then turn off, and then re-transmit
once every hour. When the vehicle reaches a speed
of 33 km/h (20 mph), the centrifugal force of the
rotating wheel closes a roll switch (inside the trans-
mitter) that powers up the Integrated Circuit.
Each transmitter has a unique identity (ID) code.
The ID code allows the module to indicate to the
driver, through the ‘‘Lo Tire’’ LCD message, that one
of the tires has lost air pressure. The DRBIII
t
is
used to tell which tire pressure sensor/transmitter
has failed or sensed a low tire pressure based on its
ID code.
Verification that the TPM system is operational
must be performed during a road test, since the
system only becomes operational when the vehicle
exceeds 33 km/h (20 mph). The DRBIII
t
must not
be connected during the road test. The DRBIII
t
can be used following the road test to check whether
or not the TPM module received RF signals. The
TPM module is located behind and right of the
Instrument Cluster.
3.12.1 TIRE PRESSURE MONITOR
MODULE
The TPM module is a microprocessor controller
that monitors the transmissions from the transmit-
ters at all times with the ignition on. The TPM
module will store the last 32 transmissions from the
tire pressure sensor/transmitters however, they
cannot be observed as they occur using the
DRBIII
t
. There are three important values in-
cluded in these transmissions. They are listed as:
why the transmission was sent, from which sensor
it came from (LF, RF, RR, LR), and the tire pres-
sure. There are four reasons why the tire pressure
sensor/transmitter will send information to the
TPM module:
Supervi-
sory This is the normal mode, the trans-
mitter will start to transmit infor-
mation to the TPM module at 33
km/h (20 mph) and continue at a
rate of one transmission per
minute.
Pressure If the pressure reading changes
more than 10.34 kpa (1.5 psi) be-
tween the normal sampling period
of 30 seconds, the transmitter will
send this change information to the
TPM module within 30 seconds.
Wake This is the very first message that
the tire pressure sensor/transmitter
sends to the TPM module. This
wake mode will only occur after the
vehicle has reached 33 km/h (20
mph).
Magnet When a magnet is placed on the
transmitter it closes a reed switch
inside the transmitter and enables
the transmitter to send a RF signal
to the TPM module. Placing a mag-
net on the transmitter would nor-
mally be done for programming
purposes when the TPM module or
the tire pressure sensor/transmitter
is being replaced.
The TPM 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 request the ‘‘Lo Tire’’ LCD
message to come on.
The TPM module performs diagnostic routines;
store Diagnostic Trouble Code(s) (DTC), and pro-
vides the system status to the Body Control Module
(BCM.) When the TPM module determines there is
a fault present, the Low Tire Pressure Signal circuit
will be pulled low (grounded.) The BCM intern
sends a PCI Bus message to the Instrument Cluster
to enable the ‘‘Lo Tire’’ LCD message. The cluster
will then send the appropriate chime message to
the BCM to sound a warning alert.
17
GENERAL INFORMATION