Aftertreatment devices are exposed to exhaust poisons from fuel, oil and coolant. Studies on fuel- and lubricant-based poisoning have been widely published. However, diesel oxidation catalyst (DOC) and catalyzed soot filter (CSF) performance after exposure to constituents of coolant is not fully understood. Exhaust gas recirculation (EGR) cooler failure can cause a coolant leak into the exhaust that can reach the exhaust aftertreatment system. Coolant contains elements that can cause deterioration of aftertreatment components. This study focuses on the poisoning effect of coolant on the performance of a DOC + CSF system. The coolant introduction simulates an engine failure such as an EGR cooler internal fracture. DOC NO oxidation, quenching and hydrocarbon (HC) slip control performance during active regenerations are evaluated after slow and after consecutive fast coolant introduction and compared to the performance before the coolant exposure. Total aftertreatment coolant exposure was equal to 1.9x and 3.8x of DOC volume for the slow and the fast coolant introduction, respectively. The DOC NO oxidation performance is negatively affected by both the slow and fast coolant injection. A decrease in NO₂ production is observed on both degreened and high-temperature-aged DOC. The DOC quenching and HC slip control experiments also confirm that the DOC performance is affected by the coolant exposure. The performance of the CSFs is also studied. Post mortem characterization of the after-treatment components that probes the distribution of the coolant elements and the catalytic deactivation as a function of the catalyst length is carried out.