How do I fix error code B3135 in a 2013 Chevrolet Equinox? I don't know where to start. It's a 2.4L engine

 

The code definition for B3135 is "All door lock circuit malfunction". A good starting point would be to check any fuses related to the Body Control Module. I didn't see any specific fuses for just the door locks so the BCM or any other computer fuses would be the next thing to check.

 

which is the scenario:
-only the drivers door lock/unlock functions are inop
-one or more but not all passenger door lock/unlock functions are inop
-all the door lock door lock/unlock functions are inop