Join Date: Nov 2003
Location: Phoenix, Arizona
Ferrari Life Posts: 366
Slow Down Light
This is a pretty standard problem on a 355. There are three thermocouples (TCs) in the exhaust system - one in each catalytic converter and one in the muffler. If the TC senses too high a temperature, it sends a signal to the computer which in turn sets the Slow Down Light. Theoretically, if you slow down, the converter will cool down. If the TC sends a "Really Hot" signal, the computer can shut down half the cylinders, which is really annoying, to keep from melting the converter.
Unfortunately, these thermocouples are also known to fail with great regularity. There's a fifty-fifty chance that there is nothing wrong with the engine, just bum TCs. The TCs cost $150 each, so it's not cheap to just throw in a new set. Furthermore, each TC's signal goes through a buffer which is also quite expensive, but not known to fail as often.
So, the big question is, is the light for real, or a false setting from a bad TC? One car I worked on, the light would come on 15 seconds after a start up, when the converter couldn't possibly have heated up that quickly. Have you seen this happen, by chance?
To be safe, I suppose you need to take it in, but be prepared to buy some new thermocouples. As long as the place isn't too far away, I think you can drive it. -Steve