NOT KNOWN FACTS ABOUT PEUGEOT ADBLUE DELETE

Since last diagnostics / code clearing drove three miles and lightweight again on / motor turned off straight away ad blue filler cap eliminated and attempted to blow/suck via cap to determine if ventilated. Cap isn't ventilated. still left cap off and tissue in filler neck for eighty miles/no lights arrived on.No, not all diesel cars use AdBlue. A