Wrangler 2WD V6-3.8L (2008)
Low Tire Pressure Indicator: Description and Operation
Operation
OPERATION
The Tire Pressure Monitor (TPM) indicator gives an indication to the vehicle operator of the status of the TPM system. The TPM indicator is controlled
by 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 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 indicator will always be OFF
when the ignition switch is in any position except ON or START. The indicator only illuminates when it is energized by the instrument cluster logic
circuit. 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 an electronic TPM indicator lamp-ON message to
the cluster to illuminate the TPM indicator for about three seconds as a bulb test.
-
TPM Indicator Lamp-On Message - Each time the cluster receives an electronic TPM indicator lamp-ON message from the SKREEM, the
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.
-
Low Tire Textual Message - On vehicles manufactured for export markets, each time the cluster receives an electronic TPM indicator
lamp-ON message from the SKREEM requesting the TPM indicator be illuminated solid, a LOtIRE textual message will appear within the
cluster odometer display. The LOtIRE textual message remains displayed 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.
-
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.
-
Actuator Test - Each time the cluster is put through the actuator test, the TPM indicator will be turned ON, then OFF again during the odometer
VFD portion of the test in order to confirm the functionality of the VFD 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.
