Low Tire Pressure Indicator - Operation

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 Controller Area Network (CAN) data bus.

The TPM indicator Light Emitting Diode (LED) is completely controlled by the instrument cluster logic circuit. This logic only allows the indicator to operate when the instrument cluster receives a battery current input on the fused ignition switch output (run-start) circuit. Therefore, the LED always 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 turns 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 TPM indicator illuminates. 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.
- 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.
- Self Test - Each time the cluster is put through the self test, the TPM indicator turns 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 low. The SKREEM then sends the proper lamp-on or lamp-off message to the instrument cluster, 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.

Use a diagnostic scan tool for proper diagnosis of the TPM system, the SKREEM, the CCN, the CAN data bus or the electronic communication related to TPM indicator operation. Refer to the appropriate diagnostic information.