Possible Causes

WARNING: This page is about a different car, the 2003 Mazda B4000, 2003 Mazda B3000, and 2003 Mazda B2300. However, it is still accessible from the selected car via links, so may be relevant.

Possible causes are:

Damaged brake switch.
Damaged PCM.
Malfunction in module(s) connected to BPP circuit.
Misadjusted brake switch.
Open or short in BPP circuit.
Open or short in brakelight circuits.