The warm absorber (WA) of NGC4051 is found to respond rapidly to the changing continuum in XMM EPIC-pn data, requiring high densities in the WA gas, so restricting the WA location The two components of the WA in NGC4051-required by RGS-the 'low' and 'high' ionization phases, are determined to lie a few light-days from the ionizing continuum source, equivalent to 2200-4400 R g. The implied mass loss rates are a few percent of the accretion rate. This suggests that AGN winds are not capable of affecting galaxy-AGN co-evolution.