A method and engine arrangement are provided for monitoring components in an exhaust aftertreatment system (EATS) including a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF), and a selective catalytic reduction catalyst (SCR). A first O2 level is measured at a first location between the DOC and the DPF, a second O2 level is measured at a second location downstream of the SCR, a first NOx level is measured at, the first location, a second NOx level is measured at the second location, SCR efficiency is calculated based on the first and second NOx levels, and whether the DOC, the DPP. and the SCR are functioning property is determined based on whether the first O2 level is within a first O:2 target, whether the second O2 level is within a second O2 target, and whether SCR efficiency is within an SCR efficiency target.