Question

Where in my 2005 Mazda Mazda6 1.8L is this module for the code B1871?

Answer 1

B1871 is for the Passenger Air Bag Disable Module Fault

if the car was in an accident the airbag(s) will have to be replaced along with the control module, and the wiring should also be checked

Answer 2

B1871 Mazda Code - Passenger Air Bag Deactivation Switch Fault
Read more: https://www.autocodes.com/b1871_mazda.html