Operation

OPERATION

The Tire Pressure Monitor (TPM) indicator gives an indication to the vehicle operator of a monitored low tire pressure condition or, in vehicles manufactured for the United States market only, 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 over the Controller Area Network (CAN) data bus from the TPM module.

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 detects that the ignition switch is in the ON position. Therefore, the LED will always be OFF when the ignition switch is in any position except ON. 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:

- Bulb Test - Each time the ignition switch is turned to the ON position the TPM indicator is illuminated by the cluster briefly as a bulb test.
- TPM Indicator Lamp-On Message - Each time the cluster receives an electronic TPM indicator lamp-ON message from the TPM module, the TPM indicator will be illuminated. In vehicles manufactured for the Unites States market only, the indicator can be flashed ON and OFF or illuminated solid, as dictated by the TPM module message. In vehicles manufactured for the Canadian market, the indicator is only illuminated solid. The indicator remains illuminated until the cluster receives a lamp-OFF message from the TPM module, or until the ignition switch is turned to the OFF position, whichever occurs first.
- TPM Textual Warning Messages - When the TPM module detects certain monitored fault conditions, it will send electronic messages requesting the cluster display a textual warning message. Each time the cluster receives an electronic textual warning request message from the TPM module, a textual message will appear within the cluster multi-function display to accompany an illuminated TPM indicator. On vehicles not equipped with the optional steering wheel buttons, a NO or a TPMS textual message may be displayed. On vehicles equipped with the optional steering wheel buttons, a Tire pres. - Adjust pres. , a Tire pres. monitor inoperative , a Tire pres. displayed after driving several minutes , a Tire pres. monitor currently unavailable , a Tire pres. monitor inoperative - No wheel sensors or a Wheel sens. missing textual message may be displayed. Refer to the owner's information packet in the vehicle glove box for more information on these textual messages.

The TPM module 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 TPM module then sends the proper lamp-ON or lamp-OFF message to the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN or KOMBI). 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 wheel sensors, the TPM module, 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.