MB09CLK

Hi, isn't it the way that a first post is usually a cry for help........lol, basically it's as the title says, just bought a 320cdi clk a month ago, thought I would try torque pro and it shows a p2138 code but isn't throwing a cel, anyone know how this can happen, the cel light is behaving normally it comes on with ignition and goes out at engine start , I cleared the code, tried a throttle reset and it came back but still no cel, any help appreciated.