Jeep Liberty KJ. Manual - part 84
TIRE PRESSURE MONITOR INDICATOR
DESCRIPTION
A Tire Pressure Monitor (TPM) indicator is standard
equipment on all instrument clusters. However, on
vehicles not equipped with the optional TPM, this indi-
cator is electronically disabled. This indicator is
located above the coolant temperature gauge and to
the right of the tachometer in the cluster overlay.
The TPM indicator consists of a stencil-like cutout of an icon that represents a cross-section of a tire with a centered
exclamation point in the opaque layer of the instrument cluster overlay. The dark outer layer of the overlay prevents
the indicator from being clearly visible when it is not illuminated. An amber Light Emitting Diode (LED) behind the
cutout in the opaque layer of the overlay causes the icon to appear in amber through the translucent outer layer of
the overlay when the indicator is illuminated from behind by the LED, which is soldered onto the instrument cluster
electronic circuit board.
The TPM indicator is serviced as a unit with the instrument cluster.
OPERATION
The Tire Pressure Monitor (TPM) indicator gives an indication to the vehicle operator of the status of the TPM sys-
tem. This indicator is controlled by a transistor on the instrument cluster circuit board based upon cluster program-
ming and electronic messages received by the cluster from the Sentry Key REmote Entry Module (SKREEM) over
the Programmable Communications Interface (PCI) data bus.
The TPM indicator Light Emitting Diode (LED) is completely controlled by the instrument cluster logic circuit, and
that logic will only allow this indicator to operate when the instrument cluster receives a battery current input on the
fused ignition switch output (run-start) circuit. Therefore, the LED will always be off when the ignition switch is in any
position except On or Start. The LED only illuminates when it is provide a path to ground by the instrument cluster
transistor. The instrument cluster will turn on the TPM indicator for the following reasons:
•
Bulb Test - Each time the ignition switch is turned to the On position, the SKREEM sends a TPM lamp-on
message to the cluster to illuminate the TPM indicator for about three seconds as a bulb test.
•
TPM Lamp-On Message - Each time the cluster receives a TPM lamp-on message from the SKREEM, the
TPM indicator will be illuminated. The indicator remains illuminated until the cluster receives a TPM lamp-off
message from the SKREEM or until the ignition switch is turned to the Off position, whichever occurs first.
•
TPM Fault Message - Each time the cluster receives a TPM fault message from the SKREEM, the TPM indi-
cator will be flashed on and off for 60 seconds indicating a sensor or system fault. The cluster then waits for
10 minutes and begins to flash the indicator again. This behavior repeats until the cluster receives a valid
message from the SKREEM indicating there is no sensor or system fault or until the ignition switch is turned
to the Off position, whichever occurs first.
•
Communication Error - If the cluster receives no TPM lamp-on or lamp-off messages from the SKREEM for
six consecutive seconds, the TPM indicator is illuminated by the instrument cluster. The indicator remains con-
trolled and illuminated by the cluster until a valid TPM lamp-on or lamp-off message is received from the
SKREEM.
•
Actuator Test - Each time the cluster is put through the actuator test, the TPM indicator will be turned on, then
off again during the bulb check portion of the test to confirm the functionality of the LED and the cluster control
circuitry.
The SKREEM performs a self-test each time the ignition switch is turned to the On position to decide whether the
TPM system is in good operating condition and whether the tire inflation pressures are too high or too low. The
SKREEM then sends the proper TPM lamp-on or lamp-off messages to the instrument cluster. For further diagnosis
of the TPM indicator or the instrument cluster circuitry that controls the indicator, (Refer to 8 - ELECTRICAL/IN-
STRUMENT CLUSTER - DIAGNOSIS AND TESTING). If the instrument cluster turns on the TPM indicator after the
bulb test, it indicates that the inflation pressure of a tire is too low or that a malfunction has occurred and the TPM
system is inoperative.
For proper diagnosis of the SKREEM, the PCI data bus, or the electronic message inputs to the instrument cluster
that control the TPM indicator, a diagnostic scan tool is required. Refer to the appropriate diagnostic information.
8J - 142
INSTRUMENT CLUSTER
KJ