I just changed the oil. Royal Purple 5W-40. So I go on a little test drive, boom. The Slow Down light comes on. WTF? (Flashes) Any ideas? It's a 1999 F355 Spider. I double checked the wiring and all looks good. I really can't slow down much when I'm at a stand still. HELP! Should I just drive it off a cliff????
drive fast let the car work and blow out all the carbon works for me every time especially the last time when i also just finished an oil change
Mine turned out to be exhaust manifold. insulation from the manfold damaged the cat..so that had to be replaced as well. My advise is don't drive it until you find the problem.
SDL is related to the catalyst protection circuit and has nothing to do with over filling the oil or having to drive the car hard to "blow out the carbon". Either you have an overheated catalyst (rare) or a fault in the system ( common). Faults are typically from either a failed catalyst ECU or temperature probe. There are many threads on how to further diagnose the issue, no sense starting over here. Just use the search function in the upper left corner of the page. Try "slow down light" searching specifically in the 348/355 section to narrow the search using "advanced search". Good luck.
Humidity also could cause the Slow Down module to fail, as the older units are becoming permeable. At least thats what the 348 Slow Down Modules in Europe are best known for. They were made from a small italian company called Vescovini and they are obsolete. They shall protect an overheat for the too-small-sized original catalytic converters and the will damage sooner or later - even if the car has not been driven, due to the age and permeability of these modules. Any dust, moisture, oil or water can penetrate them and out of the blue the slow down message will be displayed. Maybe i could help a bit. Good luck with your precious. cheers, Mike
Again, I ask the OP to search the threads for relevant information related directly to the 355. All 355s came originally with catalyst ECUs with black epoxy potting and are prone to moisture contamination. The best solution is to replace them all with the later upgraded ones, which are also used on the 360. They can be identified by the green epoxy used. I would recommend NOT purchasing used or new black epoxy ones, as they will only fail, if they arent already bad. But again, the OP does not know yet, whether he may actualy have a problem with his catalysts over heating, or bad thermo probes or the catalyst ECUs might be failing.
If you need a new thermo probe I have and extra I can sell you cheap. Replaced mine due to a CEL for the bypass valve and it turned out to be a bad valve not the thermo probe.
