Seen this issue on a few posts before and would appreciate some inputs. Its a 2000 Model Maranello 550 with a Manual G box and 35000 kms. Car was unused for about 3-4 months and the SLOW DOWN red light came on one day. Now it comes on within 2 minutes of the engine starting up. I drove the car in limp mode asusming it may burn off some excess humidity but its erratic. While driving it goes off every now and again and the car has a sudden burst of power like a turbo just kicked in. In terms of components, I understand there are 4 Oxygen sensors in this car 2 Pre cat and 2 Post Cat along with 2 ECU's. I am trying to exclude the obvious based on the symptoms. Would it be right to exclude the ECU as a possible problem as an ECU if fried would NEVER restart and the light would in theory never go off unless the ECU was replaced. The O2 sensors on the other hand may be in and out of the range if at the edge and could give faulty readings to the ECU. If the left and right are the same sensors I could just get one and try it on either side to check what make it work as an access to the SD3 means booking a car in which takes 2-4 weeks in our city. Thanks
On the 550 the Slow Down alarm is triggered only by catalytic converter overtemperatures or a fault in their circuit. For now, don't worry about the O2 sensors. Sadly, that cat overtemperature circuit is so unreliable, most of us immediately assume the slow down alarm is a false alarm and start troubleshooting the circuit, replacing the Cat ECU's and/or their thermocouples, however the right way to do this is to first figure out if the alarm is real or not. The best way to find out if it's real is via an SD2/SD3/Leonardo, where you can read the exhaust temperatures coming out of the cats. Failing that, if you have an IR gun, you can try to aim it at the same point on the cats on both sides of the car and see if you get a big difference. These IR guns are pretty fussy about the surfaces they can read from and don't like light colored, or polished surfaces, which pretty well describes the cats, so take its readings with a grain of salt. If you want to do some investigative work before putting the car on real diagnostic equipment, have a look at the Cat ECU's, which are located on the left & right sides of the fenders/structure up near the fire wall. You can't miss them and they're easy to get to. Disconnect their wires and remove the ECU's and have a look at their undersides and see if you can see cracks between the outer case and the potting compound. If there are any, moisture can find its way into the case and cause the ECU to act wonky. Some have had success with blowing hot air from a hair dryer into the cracks and/or baking them at low temperature (no more than 200F or so) in a warming oven, then filling the cracks with silicone. But it's important to figure out whether the alarm is real or not. If it's real, at the very least your engine isn't running right, and at the worst, it could be a candidate for a car fire.
Thanks for the prompt reply. The SLOW DOWN light also comes on almost 30-60 seconds after starting the engine cold 1st thing in the morning. It does not even need to go to operating temp as the engine temp needle has not even moved when the light comes on. This means it has nothing to do with the car actually heating up but some mis calculation of a temp from somewhere?
As John said. The Cat temp ECU's go bad all the time. If the light comes on when the car is cold, then one of the ECU's is probably defective.
