Low Tire Pressure

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 a transistor on the instrument cluster circuit board based upon cluster programming and electronic messages received by the cluster from the Wireless Ignition Node (WIN), over the CAN data bus.

The TPM indicator 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. Each time the ignition switch is turned to the ON position, the WIN sends an electronic TPM indicator lamp-ON  message to the cluster to illuminate the TPM indicator for about three seconds as a bulb test. The instrument cluster will turn ON the TPM indicator for the following reasons:

• TPM Indicator Lamp-On Message  - Each time the cluster receives an electronic TPM indicator lamp-ON  message from the WIN, the indicator will be illuminated. The indicator can be flashed ON and OFF, or illuminated solid, as dictated by the WIN message. The indicator remains illuminated until the cluster receives a lamp-OFF message from the WIN, 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 WIN 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 WIN.

The WIN 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 WIN then sends the proper lamp-ON or lamp-OFF message to the instrument cluster. 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.