Original: The Class 171 Turbostar is a type of diesel multiple unit (DMU) built by Bombardier Transportation (previously ADtranz) at their Litchurch Lane Works in Derby, England which is identical to the Class 170, except for the replacement of the BSI (Bergische Stahl Industrie) coupler with a Dellner coupler.
Simplified: The Class 171 is identical to the Class 170, except for the replacement of the BSI coupler with a Dellner coupler.