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 IPC circuit board based upon IPC programming and electronic messages received by the IPC from the Tire Pressure Module (TPM), over the CAN data bus.

The TPM indicator LED is completely controlled by the IPC logic circuit, and that logic will only allow this indicator to operate when the IPC 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 IPC transistor. Each time the ignition switch is turned to the ON position, the TPM sends an electronic TPM indicator lamp-ON  message to the IPC to illuminate the TPM indicator for about three seconds as a bulb test. The IPC will turn ON the TPM indicator for the following reasons:

• TPM Indicator Lamp-On Message  - Each time the IPC receives an electronic TPM indicator lamp-ON  message from the TPM, the indicator will be illuminated. The indicator can be flashed ON and OFF, or illuminated solid, as dictated by the TPM message. The indicator remains illuminated until the IPC receives a lamp-OFF message from the TPM, or until the ignition switch is turned to the OFF position, whichever occurs first.
• Communication Error  - If the IPC receives no TPM lamp-ON or lamp-OFF messages from the TPM for six consecutive seconds, the TPM indicator is illuminated by the IPC. The indicator remains controlled and illuminated by the IPC until a valid lamp-ON or lamp-OFF message is received from the TPM.

The TPM 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 then sends the proper lamp-ON or lamp-OFF message to the IPC. If the IPC 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.