OM608

When the W177 A-Class appeared in 2018, the 1.5-liter unit in the A 180 d was still the Renault K9K, redesignated OM608 in place of the OM607 that preceded it in the previous generation. Mercedes-Benz specified its own engine control unit, a stop-start system, a dual-mass flywheel and its own ancillaries; the iron block, aluminum head, single camshaft, two valves per cylinder and common-rail injection came across untouched. It produces 116 PS and 260 N·m from 1,750 rpm on a 15.1:1 compression ratio.

The suffix in its full designation, OM608 DE15 SCR, is the point of the exercise. Selective catalytic reduction — urea dosed into the exhaust to break down oxides of nitrogen — is what allowed a small diesel to remain saleable in Europe once emissions testing moved to real-world driving, and it is not a system anyone would have hung on a 1.5-liter engine by choice. Below the A 180 d, the A 180 d Sedan and the CLA 180 d there is nothing; above it sit engines Mercedes-Benz built itself. This one marks the floor of the range, and the point where the economics stopped working.