Unusual magnetoresistance observed in weak itinerant ferromagnetic metal Fe0.9Co0.1Si is addressed. We invoke localization effects significantly contributing to the positive magnetoresistance apart from quantum interference effects (QIE), a new mechanism for magnetoresistance at low temperatures. QIE are dominant only at very low temperatures while localization effects are progressive out of the sub-Kelvin domain. Dominance of localization effects in Kelvin range with increasing applied magnetic field is demonstrated. An unconventional effect of magnetic field on resistivity, favors a least dominant role of ferromagnetic correlations. The H–T phase diagram explore the regions of H3/2 (paramagnetic region) and QIE (Δσ ∝ H1/2) and its extension into the paramagnetic region. A new region of linear field dependence of MC (Δσ ∝ H) is also found and reported. Qualitative analysis of thermopower and its correspondence with electrical resistivity strengthens the concept that the same electrons are responsible for both electrical and magnetic properties. It is also reported that the onset of magnetic and QIE effects is well above TC.