A process for the production of an OEM base coat/clear top coat multi-layer coating comprising the steps: providing a substrate to be provided with an OEM base coat/clear top coat multi-layer coating, spray-applying a waterborne base coat composition on said substrate by electrostatically-assisted high speed rotary atomization to form a base coat layer, spray-applying a clear coat composition on the base coat layer to form a clear top coat layer, and jointly curing the base coat and the clear top coat layers, wherein the waterborne base coat composition comprises water, pigment(s) and resin solids consisting of binder solids and, optionally, crosslinker solids, wherein said binder solids consist of 20 to 100 wt.% of an aqueously dispersed polyurethane urea resin with a carboxyl number of 10 to 50 mg KOH/g and 0 to 80 wt.% of other binders, wherein the sum of the wt.% totals 100 wt.%, wherein said aqueously dispersed polyurethane urea resin is made by a process comprising the steps: (i) producing a non-gelled polyurethane prepolymer with a free isocyanate group content of 0.5 to 4.5 wt.% by reacting at least one polyol, at least one compound having one alcoholic hydroxyl group and a molar mass of 32 to 300, at least one polyhydroxycarboxylic acid which may or may not be neutralized with a tertiary amine, and at least one polyisocyanate, in the presence of at least one ketone and/or at least one other inert organic solvent, (ii) if not already effected, neutralizing the carboxyl group(s) of the at least one polyhydroxycarboxylic acid with a tertiary amine before carrying out step (iii), (iii) converting the so obtained ketone and/or other inert organic solvent solution of the polyurethane prepolymer into an aqueous dispersion by mixing with water, and (iv) chain extending the polyurethane prepolymer by reacting the free isocyanate groups thereof with at least one compound having at least two amino groups capable of addition to isocyanate groups to form urea groups, wherein the at least one compound having one alcoholic hydroxyl group and a molar mass of 32 to 300 is used in a proportion of 0.02 to 0.15 equivalents relative to the NCO provided by the at least one polyisocyanate employed in step (i). providing a substrate to be provided with an OEM base coat/clear top coat multi-layer coating, spray-applying a waterborne base coat composition on said substrate by electrostatically-assisted high speed rotary atomization to form a base coat layer, spray-applying a clear coat composition on the base coat layer to form a clear top coat layer, and jointly curing the base coat and the clear top coat layers, (i) producing a non-gelled polyurethane prepolymer with a free isocyanate group content of 0.5 to 4.5 wt.% by reacting at least one polyol, at least one compound having one alcoholic hydroxyl group and a molar mass of 32 to 300, at least one polyhydroxycarboxylic acid which may or may not be neutralized with a tertiary amine, and at least one polyisocyanate, in the presence of at least one ketone and/or at least one other inert organic solvent, (ii) if not already effected, neutralizing the carboxyl group(s) of the at least one polyhydroxycarboxylic acid with a tertiary amine before carrying out step (iii), (iii) converting the so obtained ketone and/or other inert organic solvent solution of the polyurethane prepolymer into an aqueous dispersion by mixing with water, and (iv) chain extending the polyurethane prepolymer by reacting the free isocyanate groups thereof with at least one compound having at least two amino groups capable of addition to isocyanate groups to form urea groups,