Tire Pressure Module: Description and Operation
TRANSPONDER - TPMDESCRIPTION
Vehicles equipped with the premium TPM system use transponders, sometimes referred to as trigger modules, to provide the Wireless Control Module (WCM), commonly referred to as the Sentry Key Remote Entry Module (SKREEM), with the location of the tire pressure sensors on the vehicle. A transponder is located in three of the four wheel wells on the vehicle The transponders are located in the left front, right front and right rear wheel wells behind the wheelhouse splash shields. Only three transponders are necessary to locate the four rotating sensors because the WCM can determine the location of the fourth by using 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 is in the left rear tire.
OPERATION
On vehicles equipped with the premium TPM system, the Wireless Control Module (WCM), commonly referred to as the Sentry Key Remote Entry Module (SKREEM), uses transponders (trigger modules) located in three of the four wheel wells on the vehicle to provide it with the location of the tire pressure sensors on the vehicle. Like the base system, the WCM receives RF signals from all four rotating wheel speed sensors. When the WCM needs to know which sensor is located at a particular location on the vehicle, it directs the transponder at that location to send out a low frequency signal to excite the nearby sensor. The WCM then receives that excited signal and knows where that sensor is located. This auto-locating process only happens in the first 10 minutes of any WCM cycle while traveling at speeds above 20 mph (32 km/h) (Each WCM cycle ends when the vehicle has been shut off for a time period of approximately 15 minutes or longer). Once the WCM has performed this to the three locations that have transponders (left front, right front and right rear wheel wells), it uses the process-of-elimination theory to know that the fourth sensor ID signal is coming from the left rear tire sensor.