Although the designation suggests a passenger locomotive, the P 4 was an express locomotive built by Maffei for the Palatine Railway in 1905 and 1906. It was based on the Bavarian S 2/5, but had a larger grate that was situated completely behind the rear driving axle. Because of this, the wheelbase between the rear driving axle and the trailing axle was made longer and the trailing axle needed a radially adjustable bearing. The driver diameter of 2,010 mm or 6 ft 7 in ensured a low rotational speed when running fast.