Gentlemen, here we are again at the virtual round table. It seems most things, the 355 are vague. Facts mix with contradicting opinions and circulated informations on the web make it very difficult to pin down the cause of a problem and come with a solution. What is on my mind today is the 355 thermocouples malfunction, the SD Light. I hope to get some facts. A thermocouples is a simple device. It’s consists of two dissimilar metals(conductors) bonded together at one end. When heat is applied to this junction, the opposite ends of the metals generate electricity. The amount of electricity generated is proportional to temperature applied. It can be used to measure temperature of equipments. This simple fact makes thermocouples useful in wide variety of applications where high fluctuating temperature sensing is crucial. One particular example is the Ferrari 355 exhaust. My questions for everyone, What is the temperature threshold of the exhaust, the point where temperature is too high and trigger a SD Light to come on? Does the ECU sense temperature threshold by the output of the voltage generated by heat measured ? If the thermocouples are disconnected, does the ECU throws a SD Light when temperature is below the threshold while engine running? If we can answer these questions factually, it is plausible and cheap to rid the SD Light forever. A lot of folks post positive experiences with after market thermocouples. I hope to understand something. The ECU throws a SD Light when exhaust reaches above a temperature set point. If the temperature reading is below that set point, the SD Light never come on. With that in mind how do we know those after market thermocouples work? We can’t just assume they work because the SD Light doesn’t come on. For argument, the thermocouples can be a piece of metal that doesn’t do anything and because it doesn’t generate a voltage, the ECU doesn’t know the exhaust temperature and never give out a SD Light. The exhaust temp. could be 1000 degrees. The ECU doesn’t know. This can be a dangerous situation. More so than a Nuisance SD Light.