Tire Pressure Monitor Indicator: Operation

WARNING: This page is about a different car, the 2005 Jeep Liberty. However, it is still accessible from the selected car via links, so may be relevant.

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:

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.
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.
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 ELECTRICAL/INSTRUMENT 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.