Diagnostic Aids
WARNING: This page is about a different car, the 2007 Pontiac G5 Pursuit, 2007 Pontiac G5, and 2007 Chevrolet Cobalt. However, it is still accessible from the selected car via links, so may be relevant.
With the use of Co-axial speakers, some sound (Bass or Treble) may be coming from the speakers depending on what circuit has been affected. Adjusting the bass and treble accordingly to identify faulty circuit may help with diagnosis.