With its 20-tonne axle load, the class 01 could not be used on many routes. Although the plans provided for the upgrading of all main routes for these loads, this project could not be implemented due to the economic crisis, and it could not have been completed within a few years. Thus, the class 03 was developed, which was almost identical in construction to the 01, but lighter.
The main changes consisted in the fact that the bar frame was now only 90 mm thick instead of 100 mm, the diameter of the cylinders was reduced from 650 to 600 mm and the pressure of the slightly smaller boiler was reduced to 14 bar. With almost identical external dimensions, an axle load of 17.7 and later 18.1 tonnes was achieved, thus significantly expanding the range of routes that could be used. After the first three examples, the boiler pressure was increased to 16 bar, analogous to most standard locomotives, but in return the diameter of the cylinders was further reduced to 570 mm.
03 001 in the year 2000 on the turntable in Dresden-Altstadt
Olaf1541 
As with the 01, the top speed was initially 120 km/h and later from the 03 163 130 km/h after the diameter of the leading wheels had been increased. Since the series was even designed for 140 km/h, some examples could also be approved for this speed after adapting the braking equipment. With a few engines, the performance in the high speed ranges could be significantly improved by using a complete or partial streamlined fairing, but this was later removed again, as was the case with the development 0310. The series machines could pull trains of 430 tonnes at 120 km/h and 790 tonnes at 100 km/h on the flat.
The three coupled axles were fixed in the frame and only the middle driven axle had wheel flanges that were 15 mm weaker. The front bogie could be moved sideways by 100 mm, the trailing axle behind the firebox was an Adams axle and had 140 mm of play. As with its heavier sister, the wheels of the bogie were 850 or 1,000 mm depending on the year of manufacture, the coupled wheels were 2,000 mm and the wheels of the trailing axle were 1,250 mm.
With a total of 298 locomotives built between 1930 and 1938, the 03 reached a larger number than the 01. After the Second World War, the West German Federal Railways received 154, the East German Reichsbahn 86 and the Polish PKP around 40 units. In the case of the latter, the engines were called Pm 2. In 1968, only 45 units were still in use on the Bundesbahn, all of which were in storage by 1972. The Reichsbahn equipped damaged locomotives with a welded firebox and feedwater heaters. The larger part of 55 engines was even completely reconstructed and provided with completely welded new boilers between 1969 and 1975. Due to the combustion chamber, they only had 5,700 mm long heating pipes instead of the 6,800 mm of the original boilers, which was already in the problematic area. They had an output increased by around 100 kW and were still used in the 1980s.