Hello, I have the following problem and hope that someone has similar experiences and can help me further: In my Toyota Yaris Verso 1.3 the yellow motor control light has been lit up again and again for 2 years. In the fault memory “Effectiveness Catalysts” is always below. Nevertheless, the car has passed the AU for the second time without any problems. The value for CO was 0.017Vol% two weeks ago. The answer from all the workshops is, of course, “First Lambda probe, then change cat and if it wasn’t, we’ll continue to see.” Of course, the bill can get longer and longer. Has anyone of you ever had such a mistake and could it be fixed and how? And does anyone know how the efficiency of the on-board electronics is determined at all? After all, the CO content before and after Kat is not measured directly; thus, parameters are read which are based on the efficiency of the on-board electronics. Is the back pressure measured in front of the cat?