A transponder, sometimes referred to as a trigger module, is located in three of the four wheel wells (behind the wheelhouse splash shields) of a vehicle equipped with Premium TPM. These transponders are used 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 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. On this vehicle, there is a transponder located in the left front, left rear, and right rear wheelhouse. There is not a transponder located in the right front wheelhouse.
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). (The auto-locating process will start again only if the vehicle has been shut off for approximately 20 minutes or longer). Once the WCM has performed this to the three locations that have transponders, it uses the process-of-elimination theory to know that the fourth sensor ID signal is coming from.
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