The DS 21 was also introduced for model year 1965. This was a 2175 cc, five main bearing engine; power was 109 hp. This engine received a substantial increase in power with the introduction of Bosch electronic fuel injection for 1970, making the DS one of the first mass-market cars to use electronic fuel injection. Power of the carbureted version also increased slightly at the same time, owing to the employment of larger inlet valves.

In 1965 a luxury upgrade, the DS Pallas (after Greek goddess Pallas), was introduced. This included comfort features such as better noise insulation, a more luxurious (and optional leather) upholstery and external trim embellishments. From 1966 the Pallas model received a driver’s seat with height adjustment.

The DS was originally designed around an air-cooled flat-six based on the design of the 2-cylinder engine of the 2CV, similar to the motor in the Porsche 911. Technical and monetary problems forced this idea to be scrapped.

Thus, for such a modern car, the engine of the original DS 19 was also old-fashioned. It was derived from the engine of the 11CV Traction Avant (models 11B and 11C). It was an OHV four-cylinder engine with three main bearings and wet liners, and a bore of 78 mm (3.1 in) and a stroke of 100 mm (3.9 in), giving a volumetric displacement of 1911 cc. The cylinder head had been reworked; the 11C had a reverse-flow cast iron cylinder head and generated 60 hp (45 kW) at 3800 rpm; by contrast, the DS 19 had an aluminium cross-flow head with hemispherical combustion chambers and generated 75 hp (56 kW) at 4500 rpm.