I've been seaching the net and found:
1) some 2011 GM cars can still learn TPMS by letting air out when in learn mode.
2) I've read that a very stong magnet (i.e. bottom of magnetic parts tray holder)
3) "The GM Tire Pressure Monitoring System (TPMS) is designed to provide information to the customer allowing them to better maintain proper tire pressure in their vehicle. Proper tire pressure is important for optimizing safety, fuel economy, vehicle performance, and tire wear. Because the GM Tire Pressure Monitoring System (TPMS) recognizes a unique sensor ID in each tire, a TPM relearn must be performed after every tire rotation.
On past model vehicles, there were two procedures to relearn the TPMS: a Dealer Procedure and a Customer Procedure. After putting the vehicle in relearn mode, the Dealer Procedure used a TPM Tool (J-46079) or equivalent to activate each TPM sensor individually (Tool Method). This allowed each rotated tire/TPM sensor ID to be stored in the new corner location. The Customer Procedure required increasing or decreasing air pressure in each tire by one psi (Delta Pressure Method) to active the sensor allowing each rotated tire/TPM sensor ID to be stored in the new corner location. When using either the Dealer or Customer Procedure, there was the possibility of picking up and storing a stray pressure sensor signal ID from another vehicle that may have been broadcasting n the area. If a stray sensor was inadvertently stored, the system would not recognize the stray sensor ID and the vehicle would set a Diagnostic Trouble Code (DTC) and illuminate the TPM System light.
To commonize procedures and eliminate the possibility of storing stray sensor signals, starting with Late 2011 Model Year GM vehicles and all vehicles build after that point will support just one TPM relearn procedure - the Dealer Procedure. This change allows both Dealers and Customers a common, faster, and more efficient method to relearn tire pressures after each tire rotation. Because all future TPM Relearns will be performed using the Dealer Procedure, customers wanting to rotate their own tires and perform their own TPM Relearn will be required to utilize a relearn tool. GM has designed and manufactured an inexpensive Relearn Tool (EL-50448) specifically for this application. Owner’s manuals have been updated accordingly, to verify the relearn method to be used, reference the Owner’s Manual – Tire Rotation – TPMS Sensor Matching Process."
