Liberty 4WD L4-2.8L DSL Turbo VIN 5 (2006)
Low Tire Pressure Indicator: Description and Operation
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 indicator 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 system. This indicator is controlled by a
transistor on the instrument cluster circuit board based upon cluster programming 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:
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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.
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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.
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TPM Fault Message - Each time the cluster receives a TPM fault message from the SKREEM, the TPM indicator 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.
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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 controlled and illuminated by the cluster until a valid TPM lamp-on or
lamp-off message is received from the SKREEM.
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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 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.
