  X-ray measurements find systematically lower Fe abundances in the X-ray
emitting haloes pervading groups ($kT\lesssim1.7$ keV) than in clusters of
galaxies. These results have been difficult to reconcile with theoretical
predictions. However, models using incomplete atomic data or the assumption of
isothermal plasmas may have biased the best fit Fe abundance in groups and
giant elliptical galaxies low. In this work, we take advantage of a major
update of the atomic code in the spectral fitting package SPEX to re-evaluate
the Fe abundance in 43 clusters, groups, and elliptical galaxies (the CHEERS
sample) in a self-consistent analysis and within a common radius of
0.1$r_{500}$. For the first time, we report a remarkably similar average Fe
enrichment in all these systems. Unlike previous results, this strongly
suggests that metals are synthesised and transported in these haloes with the
same average efficiency across two orders of magnitude in total mass. We show
that the previous metallicity measurements in low temperature systems were
biased low due to incomplete atomic data in the spectral fitting codes. The
reasons for such a code-related Fe bias, also implying previously unconsidered
biases in the emission measure and temperature structure, are discussed.
