Tire Pressure Monitoring (TPM) - Operation

OPERATION

BASE TIRE PRESSURE MONITORING

The tire pressure monitoring system (TPMS) is designed to operate without loss of function for all OEM tire construction for this vehicle. Sensors, mounted to each road wheel as part of the valve stem, transmit an RF signal indicating their individual pressure to a receiver located in the Wireless Control Module (WCM), commonly referred to as the Sentry Key Remote Entry Module (SKREEM). On a Domestic vehicle, the TPM sensor operates on a 315 MHz radio frequency. Export vehicle sensors operate on a 433 MHz radio frequency. These transmissions occur approximately once every minute at speeds over 15 mph (24 km/h). For more information on sensors, Tire Pressure Monitoring (TPM) Sensor - Operation.

If the TPM system detects that the tire pressure in any road tire is going low, beyond the Low Pressure (lamp) ON threshold (see placard table below), the TPM system will continuously illuminate an indicator lamp. If a system fault is detected, the indicator lamp will flash on/off for 75 seconds, then remain on solid.

If the WCM detects a warning or fault condition at ignition key "on" it will wait ten seconds +/- 10 % before sending the first request to illuminate the indicator lamp. This will assure that the display module has concluded its bulb check period. The display module will request a chime once per ignition cycle for each "warning" or "fault" condition detected. A "warning" or "fault" condition will remain enabled until the problem causing the condition is corrected and removed/reset.

The WCM shall continuously monitor for the receipt of tire pressure RF message transmissions from the wheel sensors during both the ignition key "on" and key "off" cycles. The wheel sensor ID's and the location of each sensor (e.g. Tire 1, Tire 2 etc.) are stored in the WCM non-volatile memory during the initial Manufacturing Plant Process, or during a service procedure, as required.

The TPM System will continue to warn the driver of low tire pressure as long as the condition exists, and will not turn off the indicator lamp until the tire pressure is at or above the Low Pressure (lamp) OFF threshold (see placard table below). The system will automatically update and the TPM indicator lamp will extinguish once the updated tire pressures have been received.

Tire pressure will vary with temperature by about 1 psi (6.9 kPa) for every 12°F (6.5°C). This means that when the outside temperature decreases, the tire pressure will decrease. Tire pressure should always be set based on cold inflation tire pressure (placard pressure). This is defined as the tire pressure after a vehicle has not been driven for more than 3 hours (and in outside ambient temperature). The tire pressure will also increase as the vehicle is driven; this is normal and there should be no adjustment for this increased pressure. For a system fault, the system will return to normal once the WCM receives a valid transmission from that sensor location.

PREMIUM TIRE PRESSURE MONITORING

The operation and lamp/chime strategy of the Base Tire Pressure Monitoring System (TPMS) also applies to the Premium TPMS, but the premium TPMS can display text messages and a tire pressure graphic display on the information cluster. If a low pressure condition is detected, in addition to a chime and indicator lamp turning ON, a graphic display of the pressure value(s) with the low tire(s) flashing will appear in the Electronic Vehicle Information Center (EVIC). Once pressure in the suspect tire(s) raises above the Low Pressure (lamp) OFF Threshold (see placard table below), the lamp will go out once the WCM receives a valid transmission from the sensor. If a system fault is detected, in addition to a chime and a indicator lamp flashing, a "Check TPM System" text message will be displayed in the instrument cluster, and the tire pressure graphic display will have "- -" in place of the pressure value. After the flash sequence, the TPM indicator lamp will remain illuminated. The system will return to normal once the WCM receives a valid transmission from that sensor location.

The Premium TPMS determines the location of the tire pressure sensors by using transponders located in three of the four wheel wells on the vehicle. A fourth transponder is not necessary in the remaining wheel well due to the process of elimination theory. Once the system knows the location of the first three sensors, it assumes the location of the fourth tire pressure sensor, and updates the graphic display when necessary. For more information, Tire Pressure Monitoring (TPM) Transponder - Operation.

For both the premium and base TPM, the recommended "Placard Pressure", "Low-pressure Threshold" and "Hysteresis Pressure Values" for the tires installed on the vehicle, are stored in the WCM non-volatile memory during the initial Manufacturing Plant Process, or during a service procedure, as required. To determine the pressure thresholds for a vehicle, refer to the Tire Inflation Pressure (Placard) Label, and then apply the placard pressure to the following table. The Low Pressure OFF Threshold is defined as the Low Pressure ON Threshold plus the Hysteresis Pressure Value.

For further information, refer to the Owners Manual or the Appropriate Diagnostic Information.

TPM THRESHOLD PRESSURES

NOTE: To determine the pressure thresholds for a vehicle, refer to the Tire Inflation Pressure (Placard) Label found on the Driver's B-Pillar, then apply the placard pressure to the following table.