It is important to have access to a TECH600Pro tool which is able to diagnose Subaru TPMS issues and also interface to the vehicle OBDII/CANbus to communicate with the vehicle Engine Control Unit (ECU) and download the TPMS IDs and their wheel locations. As an example, the TECH600Pro relearn process is as follows for the Subaru Legacy:
OBD Connect
Inflate tires to Placard
Read all sensor IDs using tool
Connect tool to OBDII port
Tool will prompt you to ensure the key is on/engine off. Following the prompts, continue through the process until tool indicates relearn successful.
If light does not go off, verify sensor modes are correct.
The tool displays the OE part number for the TPMS sensor to ensure the correct specification of replacement part is programmed.