For more than a decade now, Diamond-like carbon (DLC) coatings have been applied on internal combustion engine sliding components e.g. cam lobes, tappets, finger followers, and piston rings to reduce energy losses due to friction. These coatings are therefore lubricated with traditional engine oils that were originally developed for steel parts. However, the effect of certain additives, such as zinc-dialkyldithiophosphate (ZDDP), on the tribological behavior of DLCs is still unclear.In this work, tribological tests, surface analysis techniques, and computer simulations are combined to study the friction and wear properties of several types of DLCs in ZDDP-containing solution, as well as the underlying micro/atomistic mechanisms responsible for the observed macroscopic tribological behavior. The experiments show that for DLC/DLC contacts, the tribological behaviour in ZDDP-additivated oils can be optimized by tailoring their stiffness, surface nano-topography and hydrogen content. An optimal combination of ultralow friction and negligible wear is achieved using hydrogen-free tetrahedral amorphous carbon (ta-C) with moderate hardness. Softer coatings exhibit similarly low wear and thin ZDDP-derived patchy tribofilms, but higher friction. Conversely, harder ta-Cs undergo severe wear and sub-surface sulphur contamination. Contact-mechanics and quantum-chemical simulations reveal that shear combined with the high local contact pressure caused by the contact stiffness and average surface slope of hard ta-Cs favour ZDDP fragmentation and sulphur release. In absence of hydrogen, this is followed by local surface cold welding and sub-surface mechanical mixing of sulphur resulting in a decrease of yield stress and wear. To further investigate the effect of sulphur on the wear of hard ta-Cs, other additive molecules with and without sulphur are tested. Wear is also observed with another sulphur-containing additive, di-ter-butyl-trisulphide (TPS), while no wear occurs and ultra-low friction is maintained in Zinc dialkylphsophate (ZP), which has a similar chemical structure to ZDDP except that the sulphur atoms are replaced by oxygen. A different solution to avoid wear is by replacing one of the DLC surfaces by steel i.e. switch from DLC/DLC to DLC/steel contacts. In this case wear is avoided and friction is maintained low, thus ZDDP fulfils its role of anti-wear (AW) agent. These solutions are in line with the search of reducing friction, avoiding wear, and improving fuel efficiency of ICE in passenger cars.