A WILLING turbo-diesel engine adds to both the character and bottom-line running costs of Peugeot's 406. The spacious, smooth-riding and deft-handling European mid-size sedan (and wagon) has been around for more than six years but it has aged well and still cuts a fine figure on the road. The turbo-diesel HDi may lack the smooth, silent nature of the V6 version, but compensates with astounding economy and surprising performance. Widening the appeal, an automatic transmission is now available for both turbo-diesel sedan and wagon models.