The electromagnetic four-potential $A^mu = (Phi/c, mathbf{A})$ comprises a scalar potential $Phi$ and a vector potential $mathbf{A}$. In gauge-invariant electrodynamics, gauge symmetry together with the Lorenz condition $partial_mu A^mu = 0$ ensure that only the two transverse photon polarizations are physical, while the scalar degree of freedom decouples. Whether this elimination holds in all physical regimes is an empirical question that has never been tested in configurations where the electric field vanishes but the potentials vary in time. We ask whether the scalar mode, described by the quantity $lorenzScalar = partial_mu A^mu$, can leave a physical imprint on matter that is detectable in the electric Aharonov-Bohm effect. The original configuration proposed in 1959---time-dependent potentials applied to shielded conducting cylinders---has never been experimentally realized. We show that a phenomenological coupling $propto lorenzScalar,bar{psi}psi$ yields a phase shift proportional to $1-cos(omega T)$, orthogonal to the standard $sin(omega T)$ prediction. A frequency sweep can cleanly separate the two contributions. We outline a realistic electron interferometry experiment, analyze the dominant systematic (fringe fields), and argue that such a test is within reach of existing technology. The question is testable: a null result would provide the first empirical bound on a physical scalar mode in a field-free regime; a positive signal would indicate that the gauge-fixing procedure discards a genuine degree of freedom. Either outcome illuminates the foundations of gauge theory.