Raider 2WD V6-3.7L (2008)
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 in the speedometer dial face to the left of the speedometer needle hub in the instrument
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 indicator to appear in amber through the translucent
outer layer of the overlay when it 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) (also known as the Sentry Key Immobilizer Module/SKIM or the Wireless Control Module/WCM) over the
Controller Area Network (CAN) 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 provided 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 an electronic TPM indicator lamp-ON message to the
cluster to illuminate the TPM indicator for about three seconds as a bulb test.
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TPM Indicator Lamp-On Message - Each time the cluster receives an electronic TPM indicator lamp-ON message from the SKREEM, the TPM
indicator will be illuminated. The indicator can be flashed ON and OFF, or illuminated solid, as dictated by the SKREEM message. The indicator
remains illuminated until the cluster receives a lamp-OFF message from the SKREEM 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 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 lamp-ON or lamp-OFF message to the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab
Compartment Node/CCN). 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 ineffective.
For proper diagnosis of the TPM system, the SKREEM, the EMIC, the CAN data bus or the electronic communication related to TPM indicator
operation a diagnostic scan tool is required. Refer to the appropriate diagnostic information.
