The PSA TU engine is a family of small four-cylinder engines used in the Peugeot and Citroën range of cars. It was introduced in 1986 with the Citroën AX, replacing the X family, although it shared many components with its predecessor. The TU is available in either petrol or a non-turbo Diesel variants, the latter called TUD. The TU engine is an evolution of the X engine.The TU engine is/was used in the following cars:Citroën: AX, Saxo, C2, C3, BX, ZX, Xsara, C15, Nemo and Berlingo.