It is known from observations in space plasmas and from numerical simulations that under certain conditions, obliquely propagating shocks generate a standing whistler precursor. A one-dimensional electromagnetic implicit particle code is used to investigate its role during the cyclic reformation of quasi-parallel shocks observed in hybrid simulations. It is shown that the precursor grows until a significant number of ions become trapped, at which time the shock ramp reforms near the leading edge of the whistler wave train. Electron inertial effects are found to be rather unimportant for the reformation mechanism, although some electrons are found to be accelerated to suprathermal velocities by the whistler precursor. ¿ American Geophysical Union 1992