Possible Causes

WARNING: This page is about a different car, the 2009 Mazda 6. However, it is still accessible from the selected car via links, so may be relevant.

Open circuit in wiring harness between battery and PAD indicator
A non-standard PAD indicator bulb is installed
PAD indicator malfunction
Open or short circuit or short to ground or short to power supply in wiring harness between PAD indicator and SAS control module
SAS control module malfunction